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A.DIM
2012-Sep-27, 01:33 PM
According to new research, could be!

Slow-moving rocks better odds that life crashed to Earth from space (http://www.sciencedaily.com/releases/2012/09/120924144751.htm).

The researchers report in the journal Astrobiology that under certain conditions there is a high probability that life came to Earth -- or spread from Earth to other planets -- during the solar system's infancy when Earth and its planetary neighbors orbiting other stars would have been close enough to each other to exchange lots of solid material. The work will be presented at the 2012 European Planetary Science Congress on Sept. 25.

And the abstract:

We examined a low-energy mechanism for the transfer of meteoroids between two planetary systems embedded in a star cluster using quasi-parabolic orbits of minimal energy. Using Monte Carlo simulations, we found that the exchange of meteoroids could have been significantly more efficient than previously estimated. Our study is relevant to astrobiology, as it addresses whether life on Earth could have been transferred to other planetary systems in the Solar System's birth cluster and whether life on Earth could have been transferred from beyond the Solar System. In the Solar System, the timescale over which solid material was delivered to the region from where it could be transferred via this mechanism likely extended to several hundred million years (as indicated by the 3.8–4.0 Ga epoch of the Late Heavy Bombardment). This timescale could have overlapped with the lifetime of the Solar birth cluster (100–500 Myr). Therefore, we conclude that lithopanspermia is an open possibility if life had an early start. Adopting parameters from the minimum mass solar nebula, considering a range of planetesimal size distributions derived from observations of asteroids and Kuiper Belt objects and theoretical coagulation models, and taking into account Oort Cloud formation models, we discerned that the expected number of bodies with mass>10 kg that could have been transferred between the Sun and its nearest cluster neighbor could be of the order of 1014 to 3·1016, with transfer timescales of tens of millions of years. We estimate that of the order of 3·108·l (km) could potentially be life-bearing, where l is the depth of Earth's crust in kilometers that was ejected as the result of the early bombardment. Key Words: Extrasolar planets—Interplanetary dust—Interstellar meteorites—Lithopanspermia. Astrobiology 12, 754–774.

John Jaksich
2012-Sep-27, 04:03 PM
According to new research, could be! Slow-moving rocks better odds that life crashed to Earth from space (http://www.sciencedaily.com/releases/2012/09/120924144751.htm). The researchers report in the journal Astrobiology that under certain conditions there is a high probability that life came to Earth -- or spread from Earth to other planets -- during the solar system's infancy when Earth and its planetary neighbors orbiting other stars would have been close enough to each other to exchange lots of solid material. The work will be presented at the 2012 European Planetary Science Congress on Sept. 25. And the abstract: We examined a low-energy mechanism for the transfer of meteoroids between two planetary systems embedded in a star cluster using quasi-parabolic orbits of minimal energy. Using Monte Carlo simulations, we found that the exchange of meteoroids could have been significantly more efficient than previously estimated. Our study is relevant to astrobiology, as it addresses whether life on Earth could have been transferred to other planetary systems in the Solar System's birth cluster and whether life on Earth could have been transferred from beyond the Solar System. In the Solar System, the timescale over which solid material was delivered to the region from where it could be transferred via this mechanism likely extended to several hundred million years (as indicated by the 3.8–4.0 Ga epoch of the Late Heavy Bombardment). This timescale could have overlapped with the lifetime of the Solar birth cluster (100–500 Myr). Therefore, we conclude that lithopanspermia is an open possibility if life had an early start. Adopting parameters from the minimum mass solar nebula, considering a range of planetesimal size distributions derived from observations of asteroids and Kuiper Belt objects and theoretical coagulation models, and taking into account Oort Cloud formation models, we discerned that the expected number of bodies with mass>10 kg that could have been transferred between the Sun and its nearest cluster neighbor could be of the order of 1014 to 3·1016, with transfer timescales of tens of millions of years. We estimate that of the order of 3·108·l (km) could potentially be life-bearing, where l is the depth of Earth's crust in kilometers that was ejected as the result of the early bombardment. Key Words: Extrasolar planets—Interplanetary dust—Interstellar meteorites—Lithopanspermia. Astrobiology 12, 754–774.NIce post---I am wondering what your is your current opinion on ALH84001---and if the purported "bacterial fossils" are real or just the result from a re-liquification due to impact upon the Earth, impact upon Mars or something else? &I can remember prior posts in which "mass of approx 10 kg (?) was needed to assure that the interior of a meteor" remained in a so-called pristine state for bio-materials to not degrade to a significant manner (either during ISM transfer or impact upon the Earth) ---(that work was performed by Horneck et al of the EU)

eburacum45
2012-Sep-27, 05:03 PM
NIce post---I am wondering what your is your current opinion on ALH84001---and if the purported "bacterial fossils" are real or just the result from a re-liquification due to impact upon the Earth, impact upon Mars or something else? &I can remember prior posts in which "mass of approx 10 kg (?) was needed to assure that the interior of a meteor" remained in a so-called pristine state for bio-materials to not degrade to a significant manner (either during ISM transfer or impact upon the Earth) ---(that work was performed by Horneck et al of the EU)

One problem with the identification of fossils on ALH84001 is that the traces are too small to be Earth-like bacteria, so if they are evidence of life it appears to be radically different to anything living on Earth in the current era.
The current mainstream opinion of nanobacteria seems to be that they don't occur on Earth.
http://en.wikipedia.org/wiki/Nanobacterium

eburacum45
2012-Sep-27, 05:05 PM
I've always considered that lithopanspermia within a young star cluster is a a real possibility. Unfortunately we don't know how often abiogenesis occurs within a young star cluster- it might occur only rarely, in which case lithopanspermia would only transfer life within a few selected clusters.

John Jaksich
2012-Sep-27, 05:46 PM
One problem with the identification of fossils on ALH84001 is that the traces are too small to be Earth-like bacteria, so if they are evidence of life it appears to be radically different to anything living on Earh in the current era.The current mainstream opinion of nanobacteria seems to be that they don't occur on Earth.http://en.wikipedia.org/wiki/NanobacteriumTaking your post into consideration----I have read arguments against evidence of nano-sized bacteria---the major agrumentation runs along the following lines:liquefaction of chondritic ejecta of Mars --followed by another possible liquefaction final deposition upon the Earth---(the trip from Mars to Earth is somewhat questionable as to what happens to interiors of the SNCs . . . i.e. ALH84001) & I obviously cannot prove either one of the statements readily.

Selfsim
2012-Sep-27, 09:29 PM
Could the lithopanspermia mechanism be ruled out, if after say 5 years or so, no evidence of past life whatsoever, (fossilised), is found on Mars?

R.A.F.
2012-Sep-27, 09:53 PM
According to new research, could be!

For the moment, let's say that panspermia has been confirmed, without any question, whatsoever...


What would that mean to you, A.DIM?....what conclusions would you draw from that revelation?

What ideas not presently accepted by the mainstream would be confirmed by the discovery that panspermia actually had happened?

..and please, I know there is some reason for your advocacy of panspermia...why not share what that reason is.

Colin Robinson
2012-Sep-28, 12:06 AM
Could the lithopanspermia mechanism be ruled out, if after say 5 years or so, no evidence of past life whatsoever, (fossilised), is found on Mars?

If it were found that that meteoroids never transferred life to or from Mars, would we conclude that meteoroids have never transferred life to or from anywhere?

If we did conclude that, we would be generalizing from a sample size of one!

Noclevername
2012-Sep-28, 12:11 AM
If it were found that that meteoroids never transferred life to or from Mars, would we conclude that meteoroids have never transferred life to or from anywhere?

If we did conclude that, we would be generalizing from a sample size of one!

But by that logic we'd have to search every inch of every planet in the solar system, then every planet around every star we once shared a cluster with, to rule it out.

Colin Robinson
2012-Sep-28, 12:36 AM
But by that logic we'd have to search every inch of every planet in the solar system, then every planet around every star we once shared a cluster with, to rule it out.

That depends how far you take the idea of not generalizing. Do you go from the idea of not generalizing from a sample size of one, to not generalizing from a sample size of two, three, four etc?

Seriously, whatever is found or not found on Mars, the question of life in this solar system will not be resolved without a good look at Europa, Enceladus and Titan. And if life (or evidence of past life) is found in one or more of those places, then the next question will be how it got there. Has life emerged from non-life several times within this solar system? Or has it spread from one place in the solar system to another?

R.A.F.
2012-Sep-28, 01:47 AM
...whatever is found or not found on Mars, the question of life in this solar system will not be resolved without a good look at Europa, Enceladus and Titan. And if life (or evidence of past life) is found in one or more of those places, then the next question will be how it got there.


How far are you willing to go? meaning, when these places are checked out, and found to NOT have life, where will you extend the "goalposts"?

To the next solar system?...out to 50 light years?...100?...1000?

My point being, given this premise, you never have to concede. You can always speculate that life might be found somewhere you haven't looked yet....





Has life emerged from non-life several times within this solar system? Or has it spread from one place in the solar system to another?

It is extremely premature to ask those questions at present. Fact is, those questions are pointless until/unless other life is actually discovered elsewhere.


...and as always, I am forced to ask...What's the rush? Why not simply wait until we have a better idea of what's in our Solar System, before making speculations unsupported by any evidence?

R.A.F.
2012-Sep-28, 01:53 AM
...What's the rush? Why not simply wait until we have a better idea of what's in our Solar System, before making speculations unsupported by any evidence?

Oh, and this question is for A.DIM, too. :D

Noclevername
2012-Sep-28, 02:09 AM
Has life emerged from non-life several times within this solar system? Or has it spread from one place in the solar system to another?

How could you tell? Even if we find life with a similar biochemical basis, he Miller–Urey and similar experiments have produced a lot of the chemicals found not only in all Earth life, but many of those found specifically in DNA and RNA. Many of these compounds have also been found in lifeless meteors. So it may simply be that these chemicals are common, and that life forms out of what's readily available.

Selfsim
2012-Sep-28, 03:44 AM
Fact is, those questions are pointless until/unless other life is actually discovered elsewhere.

...and as always, I am forced to ask...What's the rush? Why not simply wait until we have a better idea of what's in our Solar System, before making speculations unsupported by any evidence?Thanks RAF! Yippee! Hallelujah...!... Made my day ... :)
(Perhaps we should consider setting a price on electrons? :) )

No matter how much speculation is dressed up as science, if its not falsifiable in practice, then it may as well be just a daydream! (And this one is!).

Selfsim
2012-Sep-28, 03:59 AM
If it were found that that meteoroids never transferred life to or from Mars, would we conclude that meteoroids have never transferred life to or from anywhere?

If we did conclude that, we would be generalizing from a sample size of one!If Mars once had 'big liquid water' and; if Mars was once a much warmer place and; if Mars endured the same bombardments as nearby Earth (at the same point in time) and; if Mars meteorites are found on Earth and; if Mars is in the habitable zone from the Sun and; if Mars had complex organic chemistry and; if Mars shows no signs of past life ... what then can be said about litho-panspermia and every other exo-life belief?

PS: Oh ... and Mars formed from the same proto-planetary disc as Earth ...

Colin Robinson
2012-Sep-28, 04:39 AM
How far are you willing to go? meaning, when these places are checked out, and found to NOT have life,

Do you really mean "when", or "if"?


where will you extend the "goalposts"?

To the next solar system?...out to 50 light years?...100?...1000?

My point being, given this premise, you never have to concede.

What do mean by "concede"?

Do you mean "concede that Earth is radically exceptional, the only planet in all the galaxies with any sort of life?"

No, I would not "concede" that, just because (which hasn't yet happened) it were established that there is no life elsewhere in our little solar system.

However, apart from thoroughly searching every planet of every galaxy, there are other forms of evidence-based argument that would lead me to concede that point, e.g.

1. if it could be shown that Earth has some special quality or attribute which is a precondition for appearance of life, and that quality or attribute does not exist anywhere else in the cosmos; or
2. if the process by which life appeared on Earth becomes so well understood, that biochemists can agree on a figure for how probable/improbable the process is. If the probability is sufficiently low, it would be reasonable to conclude that life elsewhere in the visible universe is not probable.

Regarding point 1, about 100 years ago Wallace argued that Earth may be exceptional because life is only possible near the centre of the galaxy. At that time, many astronomers thought Earth was in fact near the centre of the Milky Way galaxy; and at that time, the existence of other galaxies had not been established. So Wallace's argument, though speculative, was not unreasonable given the state of knowledge at the time. His argument is obsolete now, because we know that Earth is nowhere near the galactic centre. But it is conceivable that some future discovery might provide a basis for a similar argument.

Regarding point 2, no such reliable probability figure currently exists, because too little is known about how life got started. This may change in the future...


What's the rush? Why not simply wait until we have a better idea of what's in our Solar System, before making speculations unsupported by any evidence?

I'm of the view that speculations are a valid part of scientific discussion.

I'd point out that Isaac Asimov, whom you've quoted in your signature line, not only speculated about life beyond Earth, but also about alternative biochemistries, such as organisms whose solvent isn't water, but ammonia or methane. Please read his article

Not as We Know it – the Chemistry of Life. (http://www.bigear.org/CSMO/HTML/CS09/cs09all.htm#cs09p05)

But if you think there is something wrong with speculating, why did you ask me what conclusion would be drawn "when" Titan and Europa are established NOT to have life?

Why not simply wait until we have a better idea of what is on Titan and what is on Europa?

Colin Robinson
2012-Sep-28, 05:15 AM
If Mars once had 'big liquid water' and; if Mars was once a much warmer place and; if Mars endured the same bombardments as nearby Earth (at the same point in time) and; if Mars meteorites are found on Earth and; if Mars is in the habitable zone from the Sun and; if Mars had complex organic chemistry and; if Mars shows no signs of past life ... what then can be said about litho-panspermia and every other exo-life belief?

In that case, it could be said that

1.The probability of life emerging spontaneously on a habitable planet is less than 100 percent -- i.e. it doesn't always happen.
2.The probability of life being transferred by meteoroids from one habitable planet to a neighboring habitable planet is also less than 100 percent -- i.e. that doesn't always happen either.

It would not rule out life elsewhere, on Titan and Enceladus for instance. Nor would it rule out the possibility that meteoroids might have transferred living organisms from Titan to Enceladus, or from Enceladus to Titan.

Jens
2012-Sep-28, 05:39 AM
My point being, given this premise, you never have to concede. You can always speculate that life might be found somewhere you haven't looked yet....


I'm kind of jumping in, but I think that properly speaking, that's true. You can't decide just because you've found 100 instances where something hasn't happened that it can't happen. If you can demonstrate that panspermia is not possible for physical reasons, then you can deny it. Otherwise, you can't say "it hasn't happened," just that "it hasn't been shown to have happened."

eburacum45
2012-Sep-28, 06:24 AM
For the purposes of the fictional Orion's Arm Universe (http://www.orionsarm.com/eg-article/48e8cb5ecb84f), I've estimated that lithopanspermia between stars occurs approximately once per star-forming cluster. This rough estimate was based on an earlier paper by Adams and Spergel
http://arxiv.org/abs/astro-ph/0504648

However, this does not imply that interstellar panspermia occurs once in every cluster. On the contrary, it might happen twenty times in one out of twenty clusters, or a hundred times in 1% of all clusters. If abiogenesis inside young clusters occurs rarely, then lithopanspermia will only occur within those few clusters where abiogenesis has occured. Even if lithopanspermia is relatively common within those few clusters it could still work out to be a rare event in the galaxy as a whole.

Colin Robinson
2012-Sep-28, 07:43 AM
How could you tell? Even if we find life with a similar biochemical basis, he Miller–Urey and similar experiments have produced a lot of the chemicals found not only in all Earth life, but many of those found specifically in DNA and RNA. Many of these compounds have also been found in lifeless meteors. So it may simply be that these chemicals are common, and that life forms out of what's readily available.

How can we tell that all known living things here on Earth have a common ancestor?

There seems to be general agreement among biologists that they do have, that they are all the offspring of a single abiogenesis. I don't think there is any controversy about this in mainstream biology.

So how do they know?

I would think they take into consideration not only the chemical building blocks (like the nucleotide bases in the DNA, and the amino acids in proteins), but the overall structures and functions of the giant molecules which the building blocks go into... In other words, you don't just look at the bricks used, you look at the overall plan of the houses and factories (in this metaphor, "houses and factories" being DNA molecules and protein molecules).

Anyway, if scientists can be certain, or reasonably certain, on the basis of biochemical similarities that all Earth organisms are related, then if another related organism is found on Mars it too should be recognizable as a relative, by means of the same sort of evidence and the same sort of reasoning...

Van Rijn
2012-Sep-28, 08:22 AM
Could the lithopanspermia mechanism be ruled out, if after say 5 years or so, no evidence of past life whatsoever, (fossilised), is found on Mars?

If there's life on Mars now, I'll be surprised if solid evidence is found for it in five years.

KABOOM
2012-Sep-28, 12:08 PM
How far are you willing to go? meaning, when these places are checked out, and found to NOT have life, where will you extend the "goalposts"?

To the next solar system?...out to 50 light years?...100?...1000?

My point being, given this premise, you never have to concede. You can always speculate that life might be found somewhere you haven't looked yet....






It is extremely premature to ask those questions at present. Fact is, those questions are pointless until/unless other life is actually discovered elsewhere.


...and as always, I am forced to ask...What's the rush? Why not simply wait until we have a better idea of what's in our Solar System, before making speculations unsupported by any evidence?

What's the rush? Because there is a strong likelihood that we will all be dead long before real answers to these questions can be known (given the high cost of definitive exploration just within our own solar system). So if you are of the mindset that "speculaton" is useless until such time as proof exists, you should not waste any of your remaing earthly time on speculative debates. On the other hand, some folks view this question as a long interesting journey in which tiny little discoveries gradually move the meter (either more likely or less likely) as a multitude of factors can weigh in to support or refute well-reasoned speculative theories.

R.A.F.
2012-Sep-28, 03:32 PM
What's the rush? Because there is a strong likelihood that we will all be dead long before real answers to these questions can be known.

That's the "breaks". I'd like to live in times when the Moon is an easily accessable vacation "spot"...and that just is not going to happen in my lifetime...and I accept that.


So if you are of the mindset that "speculaton" is useless until such time as proof exists, you should not waste any of your remaing earthly time on speculative debates.

Thanks for the "advice", but I think it best if "I" choose which discussions interest me, and which do not.



On the other hand, some folks view this question as a long interesting journey in which tiny little discoveries gradually move the meter (either more likely or less likely) as a multitude of factors can weigh in to support or refute well-reasoned speculative theories.

It's like you posted...we'll likely all be long dead before there are definitive answers.

...and like I posted, that's the "breaks".

Colin Robinson
2012-Sep-29, 04:11 AM
I've been thinking further about the interesting, though speculative, scenario that at some point in the future it is established that Mars has had both liquid water and complex organic compounds, but no life...

In that case, important scientific questions would be

* nature and composition of the complex organics. How do they compare with organic material elsewhere in the solar system, e.g. on Earth and in asteroids?
* just how those complex organics have behaved on Mars. E.g. How have they interacted with each other, what sort of systems have they formed, how do those system (even though non-living) compare with the living systems of carbon compounds that exist here on Earth?

Even if Mars itself has never had life, research on the above questions might help our understanding of how come Earth has life...

Selfsim
2012-Sep-29, 07:12 AM
I think the non-finding of past life signs on Mars scenario, would highlight just how far off the mark, and in the dark we really might be, in this 'Holy Grail'-hunt for exo-life.

Given that Mars is presently portrayed as having all the attributes one would expect for an exo-life bearing planet ... and yet it it might display no signs of past life, would seriously call into question just what all this 'Habitability Zone' and liquid water inference-based rationale, is actually based upon .. and just how valid all this is, in the overall hunt for exo-life.

Even in the context of Panspermia, one would expect Mars to have gotten the same 'life-giving' bombardment as Earth did .. so how did Mars manage to kill off its 'life', even though it presumably survived prior, for hundreds of millions of years, in the extremes of a protoplanetary accretion environment? I mean if Earth received its 'dose' of living giving materials from the common bombardment, then this pre-life material must have been very hardy. Why did this suddenly cease when it fell on Mars? Wouldn't that make Mars, (or Earth), 'special' over a spatial separation of only about 50 million kms, or so? What implications would that have on Habitability Zone definitions and rationale?

Colin Robinson
2012-Sep-29, 09:05 AM
I think the non-finding of past life signs on Mars scenario, would highlight just how far off the mark, and in the dark we really might be, in this 'Holy Grail'-hunt for exo-life.

Given that Mars is presently portrayed as having all the attributes one would expect for an exo-life bearing planet ... and yet it it might display no signs of past life, would seriously call into question just what all this 'Habitability Zone' and liquid water inference-based rationale, is actually based upon .. and just how valid all this is, in the overall hunt for exo-life.

Even in the context of Panspermia, one would expect Mars to have gotten the same 'life-giving' bombardment as Earth did .. so how did Mars manage to kill off its 'life', even though it presumably survived prior, for hundreds of millions of years, in the extremes of a protoplanetary accretion environment? I mean if Earth received its 'dose' of living giving materials from the common bombardment, then this pre-life material must have been very hardy. Why did this suddenly cease when it fell on Mars?

OK, here is a speculative explanation for a speculated result -- it might, conceivably, be the case that conditions on Mars are too oxidizing for life, and have been too oxidizing since the planet was formed.

After all, life on Earth consists of molecules rich in carbon and hydrogen, and oxidization can break these molecules down into compounds like carbon monoxide, carbon dioxide, and oxidane.

Mars is already known to have at least one highly oxidizing substance in its surface sand, namely perchlorate... But the point I'm making is not just about specific substances, but the overall chemical balance of oxygen and hydrogen...

The ability of a planet to retain hydrogen has to do with how much solar radiation it gets, and also with how massive the planet is...


Wouldn't that make Mars, (or Earth), 'special' over a spatial separation of only about 50 million kms, or so?

It would make Mars and Earth different from each other, yes...


What implications would that have on Habitability Zone definitions and rationale?

Which definition, and which rationale, do you have in mind?

Selfsim
2012-Sep-29, 10:24 AM
So, the Atacama Desert, Death Valley and Antarctica all have significant perchlorate quantities in the soil there.
Yet these locations are cited as showcases for demonstrating the hardiness of extremophiles, which still seem to survive and thrive there. In fact, the atmospheric/photochemical mechanisms proposed for explaining the production of perchlorate soil salts in these locations, is also proposed for the Martian environment.

So, if life can adapt to the presence of significant quantities of perchlorate salts on Earth, why couldn't its panspermic common ancestors manage the same feat on Mars?



What implications would that have on Habitability Zone definitions and rationale?
Which definition, and which rationale, do you have in mind?What I mean is what is the point of getting all excited about exo-planet classifications like this, (http://phl.upr.edu/projects/habitable-exoplanets-catalog) when a simple oxidant in the soil chemistry (not included in the classification criteria) is put forward as an explanation for not finding life on Mars? (And that's putting aside the above mentioned contradictory argument as to why perchlorate salts should be a problem at all, for our hardy panspermic ancestors?)

Y'know, we have people here designing interstellar missions in eager anticipation of another 'Earth-like' planet showing up out thar ... but what if there's perchlorate in its soil (that can't be detected until a Phoenix-like probe takes an up-close-and-personal whiff of an exo-soil sample?)

The rationale for this whole exo-life thing is just so messed up ..!!...??... Any excuse seems to be dished up ... seemingly according to personal taste!

MaDeR
2012-Sep-29, 10:41 AM
I think the non-finding of past life signs
What are your criteria for that?

No, something that is impossible to fulfill even in case that Mars have indeed life, does not count. So no ludicrous and clearly biased conditions like "if in next five years no one will discover life on Mars, then Mars have no life at all".

If life exists on Mars, it will be at least tens meters underground. No mission currently existing or envisioned is capable of direct sampling material from that depth*. No mission like that will fly in five years. Hell, even if that mission would land today and discover something suscipious in samples, confirmation of life beyond reasonable doubt of sciencists would took at least another mission and would require MSR. Extraordinary claim requires extraordinary evidence and all of that. Five years is way too short time for that.

* In fact, autonomous drilling on another planet to that depth is probably a little outside of current technological capability of humanity.

Colin Robinson
2012-Sep-29, 11:16 AM
So, the Atacama Desert, Death Valley and Antarctica all have significant perchlorate quantities in the soil there.
Yet these locations are cited as showcases for demonstrating the hardiness of extremophiles, which still seem to survive and thrive there. In fact, the atmospheric/photochemical mechanisms proposed for explaining the production of perchlorate soil salts in these locations, is also proposed for the Martian environment.

So, if life can adapt to the presence of significant quantities of perchlorate salts on Earth, why couldn't its panspermic common ancestors manage the same feat on Mars?

Maybe the key word is "adapt"... On Earth, life seems to have first appeared when conditions were not strongly oxidizing. Later on, organisms here adapted to more oxidizing conditions. It is conceivable that on Mars, the conditions early in the history of the planet were too oxidizing for life to get started via abiogenesis, or for simple life-forms arriving via panspermia to survive...

Please note... I am not saying that any of these conjectures are true.

Mars may have had life in the past. It may have life right now... We won't know till we give it a proper study.


What I mean is what is the point of getting all excited

Who is getting excited?


about exo-planet classifications like this, (http://phl.upr.edu/projects/habitable-exoplanets-catalog)

The page you've linked to uses an Earth-similarity index which it seems to equate with planetary habitability. There are other scientists interested in this area who consider "Earth similarity" and "planetary habitability" to be two distinct questions.


when a simple oxidant in the soil chemistry (not included in the classification criteria) is put forward as an explanation for not finding life on Mars?

... as a reason why we might not find life on Mars.


The rationale for this whole exo-life thing is just so messed up ..!!...??...

What do you mean by "this whole exo-life thing"?

Do you mean any suggestion that Earth might NOT be the only planet in all the galaxies to have any sort of life on it (including the simplest of microbes)?


Any excuse seems to be dished up ... seemingly according to personal taste!

If Earth and Mars turn out to be different, in that life never appeared on Mars, I would have thought the task of science would be to work out why... It would not be a matter of dishing up an excuse, but of developing a hypothesis...

But perhaps you think there would be no need to work out why...

Rather, we should simply conclude that the very idea of life beyond this Earth is an obvious absurdity?

Selfsim
2012-Sep-29, 08:33 PM
Five years is way too short time for that.I only suggested five years because that would seem to be a reasonable estimate of Curiosity's and Opportunity's lifetime(s). It would also be sufficient time to analyse their findings, if any, and if signs of past life was abundant, and if it left fossils which have made their way to the surface.

So, a few 'ifs' there .. but hey ... after all … this is the 'if' forum isn't it? :)

Selfsim
2012-Sep-29, 09:13 PM
Maybe the key word is "adapt"... On Earth, life seems to have first appeared when conditions were not strongly oxidizing. Later on, organisms here adapted to more oxidizing conditions. It is conceivable that on Mars, the conditions early in the history of the planet were too oxidizing for life to get started via abiogenesis, or for simple life-forms arriving via panspermia to survive…You're suggesting some kind of sensitivity to initial conditions? Nah .. who'd ever accept that, now? .. :p :)
(Just kidding around!)


Mars may have had life in the past. It may have life right now... We won't know till we give it a proper study.The point is that 'proper study' is a never-ender. That's not practical when there's limited resources and other local moons/planet to explore!
We need answers! And we need them inside funding cycle timeframes (at least that's what Pamela Gay seems to recognise! .. Reference: One of her chin wags with Fraser .. can't find it just now).


Who is getting excited?The sci-fi enthusiast set!?!


The page you've linked to uses an Earth-similarity index which it seems to equate with planetary habitability. There are other scientists interested in this area who consider "Earth similarity" and "planetary habitability" to be two distinct questions.Good to hear it. Where does your mate, Chris McKay sit on this one?


What do you mean by "this whole exo-life thing"? The entire speculative topic of exo-life existence!


Do you mean any suggestion that Earth might NOT be the only planet in all the galaxies to have any sort of life on it (including the simplest of microbes)?Suggestion is one thing, but conjuring up entire Earth-like histories, like what happens here ad nauseum, as a way of talking exo-life into existence, is a completely different thing from scientific speculation.
I think you call this conjuring, 'speculation' .?.. The 'Cultural Distance Interstellar Messaging' thread is a classic current example of what isn't scientific speculation, (from where I sit).


If Earth and Mars turn out to be different, in that life never appeared on Mars, I would have thought the task of science would be to work out why... It would not be a matter of dishing up an excuse, but of developing a hypothesis...

But perhaps you think there would be no need to work out why… Why what? The existence of life on Mars IS an hypothesis! What value is there in developing another hypothesis to explain a hypothesis which is based on little more than pure speculation and imaginings?!?


Rather, we should simply conclude that the very idea of life beyond this Earth is an obvious absurdity?No .. try not worrying about it … and get on with life, exploration and learning/discussing real science, in order to develop the tools for discovering the reality of what's out there .. rather than making up endless stories which achieve little else other than maybe, entertainment for the masses.

MaDeR
2012-Sep-29, 10:50 PM
I only suggested five years because that would seem to be a reasonable estimate of Curiosity's and Opportunity's lifetime(s).
Neither Curiosity nor Opportunity was send to find life.

Van Rijn
2012-Sep-30, 12:29 AM
I only suggested five years because that would seem to be a reasonable estimate of Curiosity's and Opportunity's lifetime(s). It would also be sufficient time to analyse their findings, if any, and if signs of past life was abundant, and if it left fossils which have made their way to the surface.


Ridiculous. As I mentioned earlier, even if there is life on Mars now, I'd be surprised if solid evidence is found in five years. Given that Curiosity isn't designed for it, the evidence would have to be extremely solid and obvious, with no plausible non-life alternative explanations, or it would just be another "maybe." And the evidence would have to be where Curiosity is now, something that can be examined, not somewhere else on or under the surface of the entire planet.

Mars isn't Earth. It was always colder than Earth, and had a thick atmosphere for perhaps a billion years, so if it developed life, or had life transferred to it, it probably wasn't complex life. There might not be any easily identifiable fossils even if life was abundant at one time on the surface.




So, a few 'ifs' there .. but hey ... after all … this is the 'if' forum isn't it? :)

No, that makes no sense for your argument, namely:



Could the lithopanspermia mechanism be ruled out, if after say 5 years or so, no evidence of past life whatsoever, (fossilised), is found on Mars?

You don't rule out something on the basis of an unreasonable set of "ifs."

Again, it's obvious you aren't making a neutral "check your evidence" argument, but arguing from a position of personal incredulity.

Selfsim
2012-Sep-30, 07:00 AM
Neither Curiosity nor Opportunity was send to find life.Sure.
They do have cameras which could capture images of obvious fossils however.
Curiosity could also go way further into the chemical detail, as well.
It all depends on what is/isn't there and how self-evident (or otherwise) the specimen might be.

For a bunch of good reasons, life is speculated here to 'take off' and spread with abundance once it gets underway, isn't it?
If that is the case, then with this speculation, there should be plenty of remnants of it, shouldn't there be?
Five years would be a reasonable time to find it, I would've thought?

Colin Robinson
2012-Sep-30, 07:50 AM
Good to hear it. Where does your mate, Chris McKay sit on this one?

"Mate"? An Australian-sounding expression! Are you an Aussie, Selfsim?

Anyway, you've got it wrong, I'm afraid – the only contact I've had with Chris M. is that I once posted a couple of questions underneath an online article of his, which he was good enough to respond to. Which hardly makes us "mates"...

As for your question of whether he agrees with those who distinguish "earth similarity" from "planetary habitability"... I can only reply: I don't know...

Selfsim
2012-Sep-30, 08:15 AM
Ridiculous. As I mentioned earlier, even if there is life on Mars now, I'd be surprised if solid evidence is found in five years. Well there's nothing like a good ol' surprise to get the blood flowing, eh? :)


Given that Curiosity isn't designed for it, the evidence would have to be extremely solid and obvious, with no plausible non-life alternative explanations, or it would just be another "maybe." And the evidence would have to be where Curiosity is now, something that can be examined, not somewhere else on or under the surface of the entire planet. ... So ?? ...
... Why else was the Gale crater region chosen as the final landing site (from a selection of >~100 other sites)?
Are you saying that there was no consideration of anything related to life in that decision?

Why should it be taken for granted that Martian life exists under the surface? I was always led to understand that was just yet another speculation?

Mars isn't Earth. It was always colder than Earth, and had a thick atmosphere for perhaps a billion years, so if it developed life, or had life transferred to it, it probably wasn't complex life. There might not be any easily identifiable fossils even if life was abundant at one time on the surface.My emboldenment - all the words highlighted express speculation ... which would be your particular speculation ... which is fine by me .. it just isn't my speculation, and I'm not even attempting to try and detach you from yours ... what would be the point of trying to do that?

Its interesting to note that 'life' is based on Earth-life (because we know of no other).
Earth's extremophiles have been shown to be able to withstand extremes of temperatures, etc.
Life on Earth has survived extreme environmental shifts, as well.
In keeping with the Panspermia theme of the thread, it would seem that Earth's extremophiles might be descendants from the same life-bearing material, as was also delivered to Mars.
And yet, somehow, it is being presented that because Earth's environment is/has been different from Mars' .. now suddenly the possibility of the survival of the Martian descendants, should be taken as: "unfortunately, perhaps they didn't survive", (or evolve) .. or .. "they must've beat a hasty retreat, and headed underground".
Now why should any of that be 'taken for granted' when being compared with say, five years of accumulated hard, experimentally measured, observational evidence?



So, a few 'ifs' there .. but hey ... after all … this is the 'if' forum isn't it?
No, that makes no sense for your argument, namely:

Could the lithopanspermia mechanism be ruled out, if after say 5 years or so, no evidence of past life whatsoever, (fossilised), is found on Mars? Last time I looked, that was a question ... not an argument!


You don't rule out something on the basis of an unreasonable set of "ifs."Well, it seems many things are included on the basis of "ifs" ...
So why not rule out a few on the same basis?


Again, it's obvious you aren't making a neutral "check your evidence" argument, but arguing from a position of personal incredulity.Well, when I see some balanced neutrality, rather than rampant undisciplined speculation, the conversation might get somewhat more interesting!

I think I'm done with this thread ... adios all!

Paul Wally
2012-Sep-30, 02:30 PM
Nothing would increase the odds of panspermia like the prior occurence of terrestrial abiogenesis somewhere else. But if terrestrial abiogenesis is not sufficiently widespread, then that significantly reduces the odds of panspermia too, then it will appear that which ever way we look at it, life is more likely to arise on any given planet due to abiogenesis than due to panspermia.

The other possibility is that microbial life and complex organics can only develop under certain conditions (like space), but that these conditions are not suitable for the further evolution of life. If this is the case then that would make microbial/ complex organic panspermia a necessary requirement for the possibility of more complex lifeforms evolving under different conditions, i.e. conditions suitable for evolution but not suitable for abiogenesis. I would take the panspermia hypothesis more serious if it could be proven that there are abiogenesis conditions and evolutionary conditions, and that the two types of conditions are necessarily mutually exclusive.

The production of complex organic molecules in laboratory experiments like the Miller-Urey experiment, does however increase my confidence in the idea that the abiogenesis simply happened right here on Earth. If abiogenesis did happen on Mars billions of years ago and if there was life on the surface during that period then the current lack of evidence of complex organics on the surface is explicable on the basis that evidence should exist in the older rock strata and not on the surface. I think that's kind of the point of the Curiosity mission; to go and look at those older rock strata along Mount Sharpe.

A.DIM
2012-Sep-30, 03:05 PM
NIce post---I am wondering what your is your current opinion on ALH84001---and if the purported "bacterial fossils" are real or just the result from a re-liquification due to impact upon the Earth, impact upon Mars or something else? &I can remember prior posts in which "mass of approx 10 kg (?) was needed to assure that the interior of a meteor" remained in a so-called pristine state for bio-materials to not degrade to a significant manner (either during ISM transfer or impact upon the Earth) ---(that work was performed by Horneck et al of the EU)

Hi John.

I still tend to think we are seeing remnants of life in ALH84001. As I recall McKay et al reanalysed more rigorously their results, concluding, I think, there's no more reason to assume they are contaminants or of geologic / chemical origin than they are of biological origin. Additionally, I believe Hornek's et al work showed likely survival of microbial /bacterial spores during impact ejection events? I'll need to review to be sure, but I don't recall liquefaction playing as big a role but I'd be interested in seeing your reference.
I can agree however, it would seem the transit times are most hazardous to life surviving any transfer events, especially interstellar.
That said, I think mechanisms for lithopanspermia in or near birth clusters significantly lowers that hurdle, making interstellar transfer more plausible.

MaDeR
2012-Sep-30, 04:21 PM
They do have cameras which could capture images of obvious fossils however.
Chance of accidental encountering fossil is neligible on Earth, where life flourished in every possible niche. Fossils on Mars? If any, then microfossils only (fossilized remains of one-celled organisms). Even lower chances.


For a bunch of good reasons, life is speculated here to 'take off' and spread with abundance once it gets underway, isn't it?
If Mars ever had life, it was never as prevalent as life on Earth. It was almost certainly never multicelluar. If it is present to today, it is deep underground due to unhabitable environment on surface. No, Earth extremophiles cannot survive in these conditions. Direct exposure is no-no.


Five years would be a reasonable time to find it, I would've thought?
No, it is utterly unreasonable. I repeat: while Curiosty mission is related to life (assessing habitability of Mars now and in past), its mission is not finding life, current or exctnict. If Curiosity will not find anything indicating life, it will not mean anything for or against life being present (or in past) here, period.

Colin Robinson
2012-Oct-01, 01:29 AM
Nothing would increase the odds of panspermia like the prior occurence of terrestrial abiogenesis somewhere else. But if terrestrial abiogenesis is not sufficiently widespread, then that significantly reduces the odds of panspermia too, then it will appear that which ever way we look at it, life is more likely to arise on any given planet due to abiogenesis than due to panspermia.

The other possibility is that microbial life and complex organics can only develop under certain conditions (like space), but that these conditions are not suitable for the further evolution of life. If this is the case then that would make microbial/ complex organic panspermia a necessary requirement for the possibility of more complex lifeforms evolving under different conditions, i.e. conditions suitable for evolution but not suitable for abiogenesis. I would take the panspermia hypothesis more serious if it could be proven that there are abiogenesis conditions and evolutionary conditions, and that the two types of conditions are necessarily mutually exclusive.

Another possibility is that the places where abiogenesis can happen are a subset of habitable places. i.e. There are habitable worlds which can produce indigenous organisms and others which can't. In that case panspermia (in the sense of transfer of organisms by meteoroids) could be crucial in bringing spreading life to those habitable worlds where the conditions are not conducive to abiogenesis.


The production of complex organic molecules in laboratory experiments like the Miller-Urey experiment, does however increase my confidence in the idea that the abiogenesis simply happened right here on Earth.

The Miller-Urey experiment was a breakthrough, certainly. But that experiment used a strongly reducing atmosphere (i.e. molecules rich in hydrogen rather than rich in oxygen). There have been lots of variations tried, and, as I understand it, the general picture is that if you make the conditions less reducing, you get less synthesis of complex organics. A counter-intuitive result: to us humans, oxygen is life-giving, and yet when it comes to abiogenesis, oxygen seems to be a serious obstacle to life.

The funny part is, that the ancient atmosphere here on Earth does not seem to have been as reducing as the Miller/Urey experiment assumed (although the exact composition is still a topic of debate, and it was certainly less oxidizing that today). It seems doubtful that conditions on Earth were ever optimal for synthesis of complex organics, despite the tendency of many Earthlings to think Earth is optimal for everything to do with life.

This is not necessarily an argument against a terrestrial abiogenesis: maybe conditions don't need to be optimal for compounds to form and life to get started... However, given the argument in the OP, about the feasibility of meteoroid transfer not only within a solar system, but even within a star cluster, maybe we ought to consider the possibility that life on Earth originally came from another planet or moon with somewhat more life-giving hydrogen?

A.DIM
2012-Oct-01, 02:09 PM
I've always considered that lithopanspermia within a young star cluster is a a real possibility. Unfortunately we don't know how often abiogenesis occurs within a young star cluster- it might occur only rarely, in which case lithopanspermia would only transfer life within a few selected clusters.

Indeed, but a few clusters could mean lots of potential sites. Then again, it may be that nebulae themselves are where abiogenesis occurs. The Orion nebula appears to have all the ingredients.

A.DIM
2012-Oct-01, 03:36 PM
Indeed, but a few clusters could mean lots of potential sites. Then again, it may be that nebulae themselves are where abiogenesis occurs. The Orion nebula appears to have all the ingredients.

So I meant to include this article about what the ALMA telescope could bring to the discussion:
Astrochemistry Enters a Bold New Era (http://www.spacedaily.com/reports/Astrochemistry_Enters_a_Bold_New_Era_with_ALMA_999 .html).

transreality
2012-Oct-01, 11:34 PM
The Late Heavy Bombardment phase was due to migration of planets within the solar system, rather than any influence from the solar birth cluster, the phase of significant influx would already have been long over, presumeably that is why it is the 'late' bombardment. The Pleiades looks like an reasonably close cluster but it is less than 100my old. The Hyades is 600mya, it shows a close concentration of heavy stars in the central parsecs, the rest, the lighter stars are being ejected and dispersed, so all those stars are moving rapidly away from each other, not really a useful scenario for lithopanspermia, where the odds of any transfer would then rapidly lengthen as the cluster ages. The current estimates of life on earth require between 0.8 and 1.1 billion years to arise. So the solar cluster would already be far more dispersed than the Hyades cluster.

The 0.8myr (the fastest possible) origin coincides with the Late heavy Bombardment, not because life came in the bombardment, but because the two are mutually exclusive, the bombardment constrains the age of life. Again, by then the solar birth cluster would have been far more dispersed than the Hyades is now, and the Late Heavy Bombardment would not have been caused by interactions in the cluster, but by planetary migration.


According to new research, could be!

Slow-moving rocks better odds that life crashed to Earth from space (http://www.sciencedaily.com/releases/2012/09/120924144751.htm).

The researchers report in the journal Astrobiology that under certain conditions there is a high probability that life came to Earth -- or spread from Earth to other planets -- during the solar system's infancy when Earth and its planetary neighbors orbiting other stars would have been close enough to each other to exchange lots of solid material. The work will be presented at the 2012 European Planetary Science Congress on Sept. 25.

And the abstract:

We examined a low-energy mechanism for the transfer of meteoroids between two planetary systems embedded in a star cluster using quasi-parabolic orbits of minimal energy. Using Monte Carlo simulations, we found that the exchange of meteoroids could have been significantly more efficient than previously estimated. Our study is relevant to astrobiology, as it addresses whether life on Earth could have been transferred to other planetary systems in the Solar System's birth cluster and whether life on Earth could have been transferred from beyond the Solar System. In the Solar System, the timescale over which solid material was delivered to the region from where it could be transferred via this mechanism likely extended to several hundred million years (as indicated by the 3.8–4.0 Ga epoch of the Late Heavy Bombardment). This timescale could have overlapped with the lifetime of the Solar birth cluster (100–500 Myr). Therefore, we conclude that lithopanspermia is an open possibility if life had an early start. Adopting parameters from the minimum mass solar nebula, considering a range of planetesimal size distributions derived from observations of asteroids and Kuiper Belt objects and theoretical coagulation models, and taking into account Oort Cloud formation models, we discerned that the expected number of bodies with mass>10 kg that could have been transferred between the Sun and its nearest cluster neighbor could be of the order of 1014 to 3·1016, with transfer timescales of tens of millions of years. We estimate that of the order of 3·108·l (km) could potentially be life-bearing, where l is the depth of Earth's crust in kilometers that was ejected as the result of the early bombardment. Key Words: Extrasolar planets—Interplanetary dust—Interstellar meteorites—Lithopanspermia. Astrobiology 12, 754–774.

A.DIM
2012-Oct-02, 01:38 PM
The Late Heavy Bombardment phase was due to migration of planets within the solar system, rather than any influence from the solar birth cluster, the phase of significant influx would already have been long over, presumeably that is why it is the 'late' bombardment. The Pleiades looks like an reasonably close cluster but it is less than 100my old. The Hyades is 600mya, it shows a close concentration of heavy stars in the central parsecs, the rest, the lighter stars are being ejected and dispersed, so all those stars are moving rapidly away from each other, not really a useful scenario for lithopanspermia, where the odds of any transfer would then rapidly lengthen as the cluster ages. The current estimates of life on earth require between 0.8 and 1.1 billion years to arise. So the solar cluster would already be far more dispersed than the Hyades cluster.

The 0.8myr (the fastest possible) origin coincides with the Late heavy Bombardment, not because life came in the bombardment, but because the two are mutually exclusive, the bombardment constrains the age of life. Again, by then the solar birth cluster would have been far more dispersed than the Hyades is now, and the Late Heavy Bombardment would not have been caused by interactions in the cluster, but by planetary migration.

Hi. And thanks for the insight. I'm just now into the paper itself (found on arXiv) and am interested to see if they address what you say.
I didn't think the cause of the LHB was settled, was it? And how do we know when our sun left its cluster?

Here's another article, from Space.com (http://www.space.com/15192-sun-siblings-asteroids-earth-life.html) earlier this year, discussing exactly what we're talking about. It states, "The sun is thought to have formed around 4.5 billion years ago within a cluster of thousands of baby stars. After around 1 billion years, this cluster broke up and the sibling stars went their separate ways. But before that point, researchers say, some of these stars may have shared life in the form of bacteria or DNA molecules."

I wonder, how is it known that our sun remained in its cluster until 3.5G years ago? If that's the case, that would mean Earth too, with life on it, was within the cluster.

A.DIM
2012-Oct-04, 12:45 PM
If Mars ever had life, it was never as prevalent as life on Earth. It was almost certainly never multicelluar. If it is present to today, it is deep underground due to unhabitable environment on surface. No, Earth extremophiles cannot survive in these conditions. Direct exposure is no-no.

To be sure, direct UV exposure is a killer, and no doubt any life on Mars, now or in the past, is limited to microbes and bacteria. However, I'm not sure how deep it must be in order to survive. According to this paper (http://arxiv.org/pdf/1002.4077.pdf) some extremophiles could survive by simply being covered in dust.

eburacum45
2012-Oct-04, 01:45 PM
I wonder, how is it known that our sun remained in its cluster until 3.5G years ago? If that's the case, that would mean Earth too, with life on it, was within the cluster.

This will be an estimate based on the expected lifespan of a typical open cluster. Young open clusters are small, tightly packed and often full of gas and dust, like the Pleiades, 50 my old. Over time they will get bigger and less tightly packed, lose all their gas and dust ,and most of their big stars die young and leave white dwarfs, neutron stars or black holes behind. The Hyades is an example of an older cluster, maybe 500 my old.
After about a billion years a cluster will probably be completely dispersed, although some leave moving groups of stars behind which can be identified:
http://en.wikipedia.org/wiki/Moving_group#Moving_groups

There is a lot of variation in open cluster age, though; some clusters (such as M67) are several gigayears old and remain together for reasons unknown. We do not appear to have formed in such a superannuated cluster, and I'd guess that we left our siblings stars behind a very long time ago.

MaDeR
2012-Oct-04, 04:06 PM
some extremophiles could survive by simply being covered in dust.
Surviving as spore for few hours is not metabolizing or even, god forbid, multiplication. Forget about Martian surface (or deep space for that matter as source of abiogenesis).

Selfsim
2012-Oct-04, 10:34 PM
Surviving as spore for few hours is not metabolizing or even, god forbid, multiplication. Forget about Martian surface (or deep space for that matter as source of abiogenesis).(Ok .. so I have returned … to answer MaDer's persistent point)
So, rather than the above style of feigning an argument from unsubstantiated authority on the subject, here's a random sample of evidence supporting the panspermic transference and subsequent evolution of, extremophiles in a Martian-like environment. (Links to the actual papers can be found from the usual sources):
Mars May be Cozy Place for Hardy Microbes: (http://phys.org/news80537113.html)

In their study, the scientists tested the coldest temperature limits for two types of one-cell organisms: halophiles and methanogens. They are among a group of microbes collectively called extremophiles, so-named because they live in hot springs, acidic fields, salty lakes, and polar ice caps under conditions that would kill humans, animals, and plants. Halophiles flourish in salty water, such as the Great Salt Lake, and have DNA repair systems to protect them from extremely high radiation doses. Methanogens are capable of growth on simple compounds like hydrogen and carbon dioxide for energy and can turn their waste into methane.
Microscopic worms could hold the key to living life on Mars (http://phys.org/news/2011-11-microscopic-worms-key-life-mars.html)

The researchers were able to successfully monitor the effect of low Earth orbit (LEO) on 12 generations of C. elegans during the first three months of their six month voyage onboard the International Space Station. These are the first observations of C. elegans behaviour in LEO.

We have been able to show that worms can grow and reproduce in space for long enough to reach another planet and that we can remotely monitor their health.
The search for unusual alien life on Earth and life that can survive on Mars (http://phys.org/news159540297.html)


Another article describes exposure of an Arctic bacterial permafrost community to simulated martian conditions, including UV irradiation equivalent to about 80 days on the surface of Mars, freeze-thaw cycles, low pressure, and comparable atmospheric gas composition.

{the authors were able to} show that the bacteria were better able to survive the deeper under the surface they were found, with a 2-centimeter layer of dust offering substantial protection. Biomolecules, such as bacterial DNA and proteins, were more resistant to destruction than the bacteria themselves, as documented in the article, "Effects of Long-Term Simulated Martian Conditions on a Freeze-Dried and Homogenized Bacterial Permafrost Community." One of the broader conclusions that can be drawn from this study is that persistent long-term forward contamination is unlikely as long as bacterial cells are deposited in the upper 2 cm of the martian surface dust.

The authors present a case for how the search for weird life (life as we do not know it) can begin right here on Earth. "Alternative biochemistries may escape our current efforts tailored to characterize and identify known life," says co-author Felisa Wolfe-Simon, Postdoctoral Research Fellow at the Department of Earth and Planetary Sciences, Harvard University.
So, we have further arguments for:
- the feasibility of lithopanspemic transference of extremophiles;
- the feasibility of adaptive mechanisms of DNA molecules to handle substantial periods of UV exposure, (in terms of steady-state life-cycle periods) and;
- the 'possibility of prolonged survival and adaptation of life at depths of greater than a mere 2 cm depth (which might easily be at the bottom of drift of ice, or under a rock ledge, or under a dusty surface easily accessible by rovers with scoops, core sampling devices, etc).

Let's not forget that Viking WAS a life-detection mission also .. Curiosity may not be specifically about detecting life, but even if it was, I assert that based on Viking's track record, it wouldn't make a lot of improvement in terms of detecting hypothesised life on Mars, even if it was (based on past experience). So, why would a null life finding by Curiosity after say five years, NOT add 'weight' to the falsification of no life on Mars and non-transference via lithopanspermia mechanisms, given the amount of sample evidence likely to be gathered by Martian surface probes over the course of five 5 years? (Add to this the observation that wherever life is transferred, it seems to spread with ease)?

It seems pretty clear to me that we have next-to-no-idea about what we're looking for, where to look for it, or how it got there, in which case a random, accidental discovery made simply by the act of looking, still far outweighs any speculative hypothesis we may have dreamed up! (Which I think, also reflects the honest scientific views of most scientists).

transreality
2012-Oct-05, 01:04 AM
Microscopic worms could hold the key to living life on Mars (http://phys.org/news/2011-11-microscopic-worms-key-life-mars.html)




How does growing 12 generations of this organism over 11 days INSIDE the shirt-sleeves environment of the ISS allow the scientists to say anything about the surviveability of worms in space, let alone for millions of years. So they'll live in zero-G, big deal; so do we. Drop the temperature to 3 degress above absolute zero, remove oxygen and water, add UV and cosmic rays, apply some decent durations, then see how they survive.

when astronomers stop speculating about the ecology of organisms they know nothing about and bring some actual evidence to the table, this subject could be worth something. Just give us one observation that needs panspermia...

Selfsim
2012-Oct-05, 01:57 AM
How does growing 12 generations of this organism over 11 days INSIDE the shirt-sleeves environment of the ISS allow the scientists to say anything about the surviveability of worms in space, let alone for millions of years. So they'll live in zero-G, big deal; so do we. Drop the temperature to 3 degress above absolute zero, remove oxygen and water, add UV and cosmic rays, apply some decent durations, then see how they survive.

when astronomers stop speculating about the ecology of organisms they know nothing about and bring some actual evidence to the table, this subject could be worth something. Just give us one observation that needs panspermia...Well, even though I share to a large extent, your sentiments about valueless speculation, (which seemingly abounds, undistinguished, in this topic), their finding (http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0020459) was that the efficacy of the RNAi mechanism remains uneffected by higher than terrestrial levels of UV exposure. Further, they showed that protein degradation (a key element in muscle wasting) can be prevented by the application of RNAi against proteolytic enzymes, on Earth and in space. All this was unknown prior to the experiment.

So, if the mechanism can find a micro-environment which sustains its viability .. (and this could be at a microscopic environmental scale level), then UV may not be a problem for evolved lifeforms such as these.

In other tests, such as the ESA Expose, Biopan and Lichens experiments, (http://phys.org/news8054.html) more primitive extremophile lichens, when exposed full on to a raw space environment, survived and continued photosynthesis, in spite of 'the odds'. That may be a better example of a primitive lifeform surviving buried inside some ejected rock:

Leopoldo Sancho from the Complutense University of Madrid, indicate that lichens have the capacity to resist full exposure to the harsh space conditions, especially high levels of UV radiation. Analysis post flight showed a full rate of survival and an unchanged ability for photosynthesis.

Selfsim
2012-Oct-05, 02:10 AM
The point I'm trying to make here, is that it seems that a very large part of the 'possibility of exo-life existing' argument, relies squarely on abductive inferences drawn from related experimental evidence, of life and delivery mechanisms, and hypothetical scenarios. And yet when these very arguments are presented for the falsification case, they suddenly become 'ridiculous'?

If the 'possibility of exo-life existing' arguments are actually scientific method (as we're led to believe they are, according to some folk here), then surely the equivalent falsification arguments should be embraced with equal fervour and given equal scientific weighting ?… (Rather than being immediately shot down in flames?)

Now why does that not happen around here, I wonder? :confused:

A.DIM
2012-Oct-05, 02:30 PM
This will be an estimate based on the expected lifespan of a typical open cluster. Young open clusters are small, tightly packed and often full of gas and dust, like the Pleiades, 50 my old. Over time they will get bigger and less tightly packed, lose all their gas and dust ,and most of their big stars die young and leave white dwarfs, neutron stars or black holes behind. The Hyades is an example of an older cluster, maybe 500 my old.
After about a billion years a cluster will probably be completely dispersed, although some leave moving groups of stars behind which can be identified:
http://en.wikipedia.org/wiki/Moving_group#Moving_groups

There is a lot of variation in open cluster age, though; some clusters (such as M67) are several gigayears old and remain together for reasons unknown. We do not appear to have formed in such a superannuated cluster, and I'd guess that we left our siblings stars behind a very long time ago.
Yes, I would think so too. Do we even have candidate stars for being our star's sibling? In reading more about how the age of a cluster is figured (an equation is given pg 2 in the paper from the OP), I came across another interesting, and relevant paper: Was the sun born in a massive cluster? (http://arxiv.org/pdf/1111.3693.pdf).

What I find interesting is the "tension" between hypotheses about the sun's cluster environment. I failed to realize that for our sun to have outer planets in circular orbits fewer stars in the birth cluster are necessarily assumed, which doesn't lend to a nearby supernova (for which we have evidence).
From the Abstract: A number of authors have argued that the Sun must have been born in a cluster of no more than several thousand stars, on the basis that, in a larger cluster, close encounters between the Sun and other stars would have truncated the outer Solar System or excited the outer planets into eccentric orbits. However, this dynamical limit is in tension with meteoritic evidence that the Solar System was exposed to a nearby supernova during or shortly after its formation; a several thousand star cluster is much too small to produce a massive star whose lifetime is short enough to have provided the enrichment. ...

Were you aware of this "tension" and what do you think? I don't think we know enough just yet to safely assume our sun's birth environment. Maybe Itokawa's fragments will reveal something!

A.DIM
2012-Oct-05, 02:43 PM
Surviving as spore for few hours is not metabolizing or even, god forbid, multiplication. Forget about Martian surface (or deep space for that matter as source of abiogenesis).

This is not really about abiogenesis, is it? I didn't think so. And I don't think we know enough about how adaptable extremophiles can be. Personally, I don't think we'll have to dig deep, in certain areas, to find life on Mars.

MaDeR
2012-Oct-05, 06:00 PM
Mars May be Cozy Place for Hardy Microbes: (http://phys.org/news80537113.html)
Main problem with surface of Mars is radiation, not temperature. And from article itself we have this gem:

Our results show that the lowest temperatures at which these organisms can thrive fall within the temperature range experienced on present-day Mars, and could permit survival and growth, particularly beneath Mars’s surface.
Nowhere in this article radiation issue is addressed (rightly so, as this article was about something else). No, surviving "extremely high radiation doses" (whatever this means in context of martian surface environment) does not count, as I said in previous post.


Microscopic worms could hold the key to living life on Mars (http://phys.org/news/2011-11-microscopic-worms-key-life-mars.html)
Transreality already commented about non-sequitureness of this piece.


The search for unusual alien life on Earth and life that can survive on Mars (http://phys.org/news159540297.html)
You cited that "bacteria were better able to survive the deeper under the surface they were found". This confirms my claim that we will have to dig deeper. And yet again, "2-centimeter layer of dust offering substantial protection" does not mean anything above "bacteria were able to survive a little longer". I commented about mere survival in previous post.

You are fond to make 50 meter deep mountains from 2 cm under surface molehills, aren't you?


So, why would a null life finding by Curiosity after say five years, NOT add 'weight' to the falsification of no life on Mars and non-transference via lithopanspermia mechanisms, given the amount of sample evidence likely to be gathered by Martian surface probes over the course of five 5 years?
To be it significant and adding any weight whatsoever, you would have to prove that:
assuming life on Mars exists, there is high probability that there is evidence of life in samples gathered from surface in few small samples from one semirandom place out of entire planet.

Final word:
Your claim is completely damned anyway, as there is no way that any life-indicating result from single mission would be taken at face value. Mounting at least one new mission, taking samples, flyng back to Earth with them and researching them would take way longer than 5 years from initial discovery (let alone from now). So your condition is pure bunk from any possible angle.

Colin Robinson
2012-Oct-06, 10:54 AM
Let's not forget that Viking WAS a life-detection mission also ..

"Also"??

Actually Viking was the only space mission ever with equipment designed for life-detection.


Curiosity may not be specifically about detecting life, but even if it was, I assert that based on Viking's track record, it wouldn't make a lot of improvement in terms of detecting hypothesised life on Mars, even if it was (based on past experience). So, why would a null life finding by Curiosity after say five years, NOT add 'weight' to the falsification of no life on Mars and non-transference via lithopanspermia mechanisms, given the amount of sample evidence likely to be gathered by Martian surface probes over the course of five 5 years?

Well, it's certainly possible that the results of the Curiosity mission will make present and/or past life on Mars seem less likely... or (for that matter) more likely.


(Add to this the observation that wherever life is transferred, it seems to spread with ease)?

If you or I were transferred to the Sahara desert, would we spread with ease?

I think not, because water is important to us, and the supply of water in the Sahara is limited...


It seems pretty clear to me that we have next-to-no-idea about what we're looking for, where to look for it, or how it got there, in which case a random, accidental discovery made simply by the act of looking, still far outweighs any speculative hypothesis we may have dreamed up!

Does that mean we don't need to think about where to look or how to look, we should just look at random?

Paul Wally
2012-Oct-06, 04:28 PM
The purpose of the Curiosity mission is to check for past habitability on Mars, that is according to our current understanding of "habitable". If it turns out that Mars was habitable then the next question is whether there actually was life. I don't know whether Curiosity is equipped to answer the question of life existence; at best I think the evidence would be highly suggestive but inconclusive, in the case of a habitable outcome. So in this case I think follow-up missions will definitely be required.

If however, it turns out that Mars was never habitable, then we have to consider the possibility that there never was any life on Mars, past and present. Scientific priorities will probably begin to shift away from searching for life on Mars. There will probably still be scientists developing alternative theories of habitability, and on that basis postulate possible life on Mars. But unless there are strongly suggestive evidence, any follow up missions will probably not be designed around such hypotheses. I think in the case of non-past habitability outcome, priorities will begin to shift towards the question of whether life can be introduced into the Martian environment or how that could possibly be achieved, i.e. terraforming.

Selfsim
2012-Oct-06, 09:35 PM
If you or I were transferred to the Sahara desert, would we spread with ease?

I think not, because water is important to us, and the supply of water in the Sahara is limited…As well as humans, there are also many other species related to humans, which survive even in that arid environment. And what's more, they could easily be detected by the instrumentation of a Curiosity type rover.
(I'm somewhat surprised by your choice of the Sahara .. I would've thought the arid regions of the Atacama Desert, Death Valley and Antarctica would have been a better chemical/environmental match to Mars conditions .. and yet those regions are also home to many detectable extremophile species, who are not necessarily native to those areas. Even in the case of where they are 'native' to those areas, at some time, (in some past phase of pre-life chemistry, or shortly thereafter), their fundamental constituents allowed them to adapt .. and these mechanisms, (such as RNAi), exist at the core of all 'life').

Your ideas about following the chemically and environmentally complex trail of breadcrumbs would also seem to be questionable, given that chemical complexity also occurs in free space (?)


Does that mean we don't need to think about where to look or how to look, we should just look at random?No … it just means that, in my view, science's present state of understanding about hypothesised exo-life is still in the 'dreaming' stages. The inferences drawn upon to argue exo-life into existence, mean virtually nothing until a chance discovery occurs, and that applies irregardless how much abductive inference based logic is applied to the argument (which, I might add, seems more specifically intended to merely win an argument, as opposed to address the central issues). Actively investing in such research, (like remote exo-life detection over light year distances, building interstellar spacecraft, panspermia experiments, etc), would also seem to make little difference in terms of providing useful informational returns about exo-life (if it exists), because of its inability to return the hard information to where interpretation can be subsequently developed, when compared with the alternative of exploring local Solar system planets, moons and asteroids ...

Colin Robinson
2012-Oct-06, 11:38 PM
As well as humans, there are also many other species related to humans, which survive even in that arid environment. And what's more, they could easily be detected by the instrumentation of a Curiosity type rover.
(I'm somewhat surprised by your choice of the Sahara .. I would've thought the arid regions of the Atacama Desert, Death Valley and Antarctica would have been a better chemical/environmental match to Mars conditions .. and yet those regions are also home to many detectable extremophile species, who are not necessarily native to those areas. Even in the case of where they are 'native' to those areas, at some time, (in some past phase of pre-life chemistry, or shortly thereafter), their fundamental constituents allowed them to adapt .. and these mechanisms, (such as RNAi), exist at the core of all 'life').

Any of these arid regions may be compared to Mars up to a point. They are all sparsely populated in comparison to the Amazon rainforest or the Great Barrier Reef. Availability of water is a limiting factor...


Your ideas about following the chemically and environmentally complex trail of breadcrumbs would also seem to be questionable, given that chemical complexity also occurs in free space (?)

I claim no personal credit for the idea that life involves complex chemistry... Actually, one thing Curiosity is designed to do, is to look for carbon-chain molecules.

Yes, there are various places, including asteroids, where complex molecules can be found. But there are other questions to consider, like...

* Where is liquid water available?
* Where has liquid water been available in the past?
* Are there other solvents that could function instead of liquid water in a living system?
* Would it be possible for living things to exist without a solvent?

Another very important question:

* Is everything at equilibrium, or is there a flow of chemical energy?
* Would it be possible for living things to exist without an energy source?


No … it just means that, in my view, science's present state of understanding about hypothesised exo-life is still in the 'dreaming' stages. The inferences drawn upon to argue exo-life into existence, mean virtually nothing until a chance discovery occurs, and that applies irregardless how much abductive inference based logic is applied to the argument

What do you mean by "abductive inference based logic"? How is your critique of it relevant to what we are discussing?

Selfsim
2012-Oct-07, 09:18 AM
Any of these arid regions may be compared to Mars up to a point. They are all sparsely populated in comparison to the Amazon rainforest or the Great Barrier Reef. Availability of water is a limiting factor…Well, it might be equally said: "So is looking for Earth-like life on Mars"!

It is this initial premise, which demands the presence of liquid water in the first place ... and what now drives the search for such 'life' underground on Mars!

Why not just say that the intial inference-based premise was likely to have been flawed in the first place? After all, there was never any specific non-Earth based evidence, to suggest it was ever a valid premise for Mars anyway.


... Actually, one thing Curiosity is designed to do, is to look for carbon-chain molecules.… the SAM package ? … Yet another experiment tuned to specifically look for 12C/13C isotopic ratios, also … which is a very specific test for-Earth-like life. (Just pointing out contrary evidence to the argument that Curiosity is supposedly not a 'life detection' mission .. clearly this is not so, when viewed from a dispassionate perspective about one of Curiosity's real design capabilities ..otherwise, what else would be the purpose of such an experiment?).


Yes, there are various places, including asteroids, where complex molecules can be found. But there are other questions to consider, like…

* Where is liquid water available?
* Where has liquid water been available in the past?
* Are there other solvents that could function instead of liquid water in a living system?
* Would it be possible for living things to exist without a solvent?
All of which just raises the complexity level, which in isolation, means not much at all (in the absence of other inferenced based logic) .. and which may also merely be coincidental, in our specific life case.

Another very important question:

* Is everything at equilibrium, or is there a flow of chemical energy?Equilibrium may also only be a 'fleeting' state in observably oscillating, (or perturbed), dynamic systems when observed over longer (or shorter) timeframes .. which are quite a common phenomenon, too … in other words, I'm not convinced that the chemical energy gradient characteristic is unique only to life's particular chemical variant, (and I don't think I'd be alone in that view, either).

Thus, exactly what makes this such a 'very important' question?

* Would it be possible for living things to exist without an energy source?I find this question to be so extreme, to be almost self-redundant .. (no offence intended here, by the way).


What do you mean by "abductive inference based logic"? How is your critique of it relevant to what we are discussing?Mr Wally has pointed out in previous threads, that this is effectively the basis of most scientific theory, (and I think I agree with that point). However, whenever the same logic is applied to falsification of hypotheses dreamed up to explore certain speculations, it is almost immediately dismissed as ATM (or flawed logic). I suspect the panspermia arguments (tenaciously raised by A.DIM), suffer this fate just about everytime he makes a post about the 'evil' panspermia perspective? (It would be interesting to hear A.DIM's perspective on this sometime).

In terms of its relevance here, the OP raised a new study outcome, (and I have supplemented with the typical other 'evidence'), for panspermia in this thread. All these arguments combined seem to set the expectation that life should exist on Mars. Rover and probe experiments have been specifically designed, and deployed to find it. And yet, even prior to Curiosity's organics investigations commencing, we are somehow also being led towards expecting 'no-life' to be found, where lithopanspermia would have deposited it. This is even in spite of the inference based evidence that Earth-like extremophiles could evolve and survive on the surface. I find this reasoning inconsistent. Either inference based rationale is acceptable for leading towards a 'likely' expectation of life on the surface (which still seems to have evidence in support of it).. and if life is not found, then something could equally be amiss in the inference style arguments which originally led to this expectation. Merely reformulating a different sub-terrainian life dwelling hypothesis, (making full use of the same style of inference), avoids justifying why such inference methods should be paid further attention at all in topics utterly devoid of precedent, (or prior data).

To me, inference based logic is more like a tactic for winning an argument ... as opposed to a useful method for discovering physical reality(?).

Why not use a null life finding on Mars (should that occur), to review our heavy reliance on such logic, especially in cases where there is an absence of any hard data?

Paul Wally
2012-Oct-07, 02:52 PM
… the SAM package ? … Yet another experiment tuned to specifically look for 12C/13C isotopic ratios, also … which is a very specific test for-Earth-like life. (Just pointing out contrary evidence to the argument that Curiosity is supposedly not a 'life detection' mission .. clearly this is not so, when viewed from a dispassionate perspective about one of Curiosity's real design capabilities ..otherwise, what else would be the purpose of such an experiment?).

The purpose of the experiment would still fall within the objective of answering the question of habitability, because evidence of life would imply habitability, but evidence of habitability does not necessarily imply life. If Curiosity was a purely life-detection mission and no such life is found, the question of habitability would still remain unanswered. But if we can first answer the question of habitability with a yes, then the next question is whether there actual was life. It makes sense, if they could get a better idea of the past habitable conditions they will be better able to design life-detection experiments for life postulated to exist under those conditions.





Equilibrium may also only be a 'fleeting' state in observably oscillating, (or perturbed), dynamic systems when observed over longer (or shorter) timeframes .. which are quite a common phenomenon, too … in other words, I'm not convinced that the chemical energy gradient characteristic is unique only to life's particular chemical variant, (and I don't think I'd be alone in that view, either).

It may be a necessary but not sufficient (unique) characteristic of life. So, if some necessary characteristic is not found then it will at least rule life out for that particular experiment. But if multiple necessary characteristics of life are found and they are found to be correlated in some such way that could only be explained by life, then either it is an amazing coincidence of life-characteristics coming together in one place, or it simply is life.



Why not use a null life finding on Mars (should that occur), to review our heavy reliance on such logic, especially in cases where there is an absence of any hard data?

A null life finding in combination with a positive finding for habitability will be a very interesting outcome. It could for instance mean that we have to review our theory of habitability, i.e. Mars used to be habitable but why was there no life? It could also test panspermia hypothesis, e.g. if Mars was habitable why didn't life spread from Earth to Mars? So, my point is, we don't have to review our scientific methodology, because it is by its very nature revisionary.

marsbug
2012-Oct-07, 05:48 PM
Just to point out: Liquid water is indeed possible under the martian range of atmospheric pressures (1mbar to 15 mbar) and temperatures (ground temperatures exceeding freezing in many areas). Since the martian atmosphere is CO2, not water vapour, any liquid phase would be only metastable (rapidly evaporate), but there is nothing that rules out its occurence if near surface ice were exposed in the right spot.

The problem is that getting any large amount to hang around, for more than minutes, would need some sort of special pleading (Eg stabilising salts in solution with it). Such special pleading conditions are not beyond all possibility - appropriate salts, for example, are known to exist on Mars.

Radiation tolerant organisms are well known, and as has been pointed out, only centimeters of Martian dust are needed to sheild microbes from UV. It's a long shot, but I don't think we can totally debunk the idea of a habitable surface, or near surface, niche on Mars....yet.

Colin Robinson
2012-Oct-07, 08:57 PM
Just to point out: Liquid water is indeed possible under the martian range of atmospheric pressures (1mbar to 15 mbar) and temperatures (ground temperatures exceeding freezing in many areas). Since the martian atmosphere is CO2, not water vapour, any liquid phase would be only metastable (rapidly evaporate), but there is nothing that rules out its occurence if near surface ice were exposed in the right spot.

The problem is that getting any large amount to hang around, for more than minutes, would need some sort of special pleading (Eg stabilising salts in solution with it). Such special pleading conditions are not beyond all possibility - appropriate salts, for example, are known to exist on Mars.

Radiation tolerant organisms are well known, and as has been pointed out, only centimeters of Martian dust are needed to sheild microbes from UV. It's a long shot, but I don't think we can totally debunk the idea of a habitable surface, or near surface, niche on Mars....yet.

I agree. Mars today may get liquid water periodically, for instance under the surface, and with perchlorate salts functioning as antifreeze. And that water may support a population of living organisms.

When I raised the point about liquid water availability as a limiting factor, I was making the point that water-based life on Mars today, if it does exist, is likely to be sparse in comparison with life on any region of Earth (including Antartica and Death Valley).

Again, it is very possible that past Mars had much more water, and could have supported a much larger population of water-needing organisms. However, it will not be easy to identify the remains of even a large population of organisms from billions of years ago. You'd come up against the problem of distinguishing between microbial fossils and nonbiologically-produced structures in rock, just as in the case of that Martian meteorite AH84001 found in Antartica.

So I don't think we can expect quick answers, either negative or positive, regarding either present or past life on Mars.

Selfsim
2012-Oct-07, 10:15 PM
The purpose of the experiment would still fall within the objective of answering the question of habitability, because evidence of life would imply habitability, but evidence of habitability does not necessarily imply life. Small nitpick: it seems so easy to make statements like the underlined one and yet, how does one know this as a fact? Presumably, (from the following statement, the idea might be to investigate further about whether evidence of habitability might/might not imply life? (That is, if habitability is determined) ..


If Curiosity was a purely life-detection mission and no such life is found, the question of habitability would still remain unanswered. But if we can first answer the question of habitability with a yes, then the next question is whether there actual was life. It makes sense, if they could get a better idea of the past habitable conditions they will be better able to design life-detection experiments for life postulated to exist under those conditions.Which would still imply that 13C/12C tests are about moving in the direction of ultimately detecting life(??)
However, in retrospect, I do realise that the test can also be used as a way of tracing where any water found in a sample originated (atmosphere, ground, carbonate, etc). The test is not only used as a way of determining what food Earth-like-life might be metabolising. If I recall correctly, I think it was also used to determine whether the origin of Glycine (found in the Stardust sample return mission, of comet Wild 2), was terrestrial contamination (or not) .. a handy test for several reasons, I think.

Either way, such tests could be able to be used as a way of determining the origin of any asteroids suspected of being deposited via lithopanspermia means, I suppose (?)


A null life finding in combination with a positive finding for habitability will be a very interesting outcome. It could for instance mean that we have to review our theory of habitability, i.e. Mars used to be habitable but why was there no life? It could also test panspermia hypothesis, e.g. if Mars was habitable why didn't life spread from Earth to Mars? So, my point is, we don't have to review our scientific methodology, because it is by its very nature revisionary.Do you consider inference to be part of scientific methodology? .. that's interesting … (and slightly disturbing).

Noclevername
2012-Oct-07, 11:29 PM
A null life finding in combination with a positive finding for habitability will be a very interesting outcome. It could for instance mean that we have to review our theory of habitability, i.e. Mars used to be habitable but why was there no life?

There is always the possibility that life does not always happen even in potentially habitable conditions. There are far too many unknown (or known but random) factors to come to any definitive conclusions.


It could also test panspermia hypothesis, e.g. if Mars was habitable why didn't life spread from Earth to Mars?

Because no life from Earth made it to Mars? If panspermia is possible doesn't mean it happens every time.

Selfsim
2012-Oct-08, 03:14 AM
I agree. Mars today may get liquid water periodically, for instance under the surface, and with perchlorate salts functioning as antifreeze. And that water may support a population of living organisms.

When I raised the point about liquid water availability as a limiting factor, I was making the point that water-based life on Mars today, if it does exist, is likely to be sparse in comparison with life on any region of Earth (including Antartica and Death Valley). Just as a reminder, the original discussion was about surface based Earth-like Martian life. In this almost totally unconstrained conversation, it could be equally possible that abundant Earth-like subterranean Martian life exists. In which case a mechanism like volcanism, might bring evidence of it, (or its past existence), to the surface for something like Curiosity to find.
As a footnote: these conversations are so unconstrained, I find them to be almost pointless, due to a complete lack of relevant data.


Again, it is very possible that past Mars had much more water, and could have supported a much larger population of water-needing organisms. However, it will not be easy to identify the remains of even a large population of organisms from billions of years ago. You'd come up against the problem of distinguishing between microbial fossils and nonbiologically-produced structures in rock, just as in the case of that Martian meteorite AH84001 found in Antartica.Yet again we see the scenario of a large past population being hypothesised, yet somehow, leaving indistinguishable, 'sparse' evidence of its prior existence. Why this particular scenario(?) Especially if this is as equally unlikely, as it is likely. In the case of Martian meteorites discovered on Earth, there is a complete lack of natural surroundings/ environmental data, pertaining to the origin of the meteorites, prior to their arrival(s). Eliminating this particular problem, would seem to be the prime purpose of all those instruments aboard Curiosity being delivered to where they were delivered (Gale crater). The case of ALH84001 found in Antarctica, is completely not relevant, due to the lack of supporting evidence of prior native environmental surroundings, of the sample. Ignoring this aspect, would undermine the integrity of the assertion that 'other' physical evidence leads to a valid inferenced-based hypothesis.

Curiosity has not yet gathered its data, and yet for some reason we seem to be preparing explanations for a negative finding. Why, I ask?


So I don't think we can expect quick answers, either negative or positive, regarding either present or past life on Mars.And I think that might be based on pure opinion (owing to the lack of relevant data …)

Colin Robinson
2012-Oct-08, 11:40 AM
Just as a reminder, the original discussion was about surface based Earth-like Martian life.

This thread was originally about the prospect of meteoroid transfer of life within a star cluster... How is surface life on Mars any more relevant to this than sub-surface life?


Curiosity has not yet gathered its data, and yet for some reason we seem to be preparing explanations for a negative finding. Why, I ask?

Perhaps it has something to do with the question raised by you, in post #6 of this thread...


Could the lithopanspermia mechanism be ruled out, if after say 5 years or so, no evidence of past life whatsoever, (fossilised), is found on Mars?

You raised this question. Now you want to know why others have responded to it?

Paul Wally
2012-Oct-08, 03:32 PM
Small nitpick: it seems so easy to make statements like the underlined one and yet, how does one know this as a fact?

We know that for a fact because it follows by logical inference from the meaning of the word "habitable". If you believe this is something that needs to empirically investigated, then it is also no wonder you find inference as part of scientific methodology disturbing.




There is always the possibility that life does not always happen even in potentially habitable conditions. There are far too many unknown (or known but random) factors to come to any definitive conclusions.

That's a valid point. A planet could for instance be habitable but abiogenesis didn't happen for some reason or panspermia didn't occur, even though conditions suitable for life do exist.




Because no life from Earth made it to Mars? If panspermia is possible doesn't mean it happens every time.

Sure, I think panspermia is possible, it's just a question of whether it is something that is very likely to happen anywhere. If Earth had life on it and Mars was habitable for a sufficiently long time, say a billion years, then life not being deposited on Mars during that habitable period must at least say something about the likelihood of such a transfer.

Noclevername
2012-Oct-08, 03:48 PM
Sure, I think panspermia is possible, it's just a question of whether it is something that is very likely to happen anywhere. If Earth had life on it and Mars was habitable for a sufficiently long time, say a billion years, then life not being deposited on Mars during that habitable period must at least say something about the likelihood of such a transfer.

One example of non-transfer is not enough to draw a conclusion.

Selfsim
2012-Oct-08, 08:09 PM
This thread was originally about the prospect of meteoroid transfer of life within a star cluster... How is surface life on Mars any more relevant to this than sub-surface life?Well, how did sub-surface life get to the sub-surface, if lithopanspermia didn't deposit life on the surface first?
(Given the context of this thread being about lithopanspermia .. not abiogenesis?)


Perhaps it has something to do with the question raised by you, in post #6 of this thread…So my asking a simple question results in the creation of a huge story in defence of some 'possibility', when there was absolutely no evidence to suggest it was ever more than a story?

Selfsim
2012-Oct-08, 08:14 PM
We know that for a fact because it follows by logical inference from the meaning of the word "habitable". If you believe this is something that needs to empirically investigated, then it is also no wonder you find inference as part of scientific methodology disturbing.Well y'know Paul … I think we're finally getting somewhere! :)
Under certain circumstances, deduction can result in correctness .. but not so with inference.


Sure, I think panspermia is possible, it's just a question of whether it is something that is very likely to happen anywhere. If Earth had life on it and Mars was habitable for a sufficiently long time, say a billion years, then life not being deposited on Mars during that habitable period must at least say something about the likelihood of such a transfer.Well what exactly must it say about it (in terms of the broader generalised theory about exo-life, which you've mentioned in the past, which you say is feasible)?

Colin Robinson
2012-Oct-08, 10:40 PM
So my asking a simple question results in the creation of a huge story in defence of some 'possibility', when there was absolutely no evidence to suggest it was ever more than a story?

This thread is about meteorite transfer of life. Is such an event more than a story? Scientists (for instance those quoted in the OP) have argued that it is a "story" consistent with what we know about meteoroids, and with what we know about microbes.


Well, how did sub-surface life get to the sub-surface, if lithopanspermia didn't deposit life on the surface first?
(Given the context of this thread being about lithopanspermia .. not abiogenesis?)

You are asking me for another story?

Fine, here are two stories for you...

1. Actually, lithopanspermia did bring life to the surface first, around 4 billions years ago, when conditions on Mars and Earth were quite similar. Back then, both planets had thick atmospheres, lots of water, and (thanks to the lithopanspermia) lots of very similar microbial life. In those days, it was all over the surface and extended quite deep underground (as in the case of Earth today). As the atmosphere of Mars got thinner, the surface got dryer and more irradiated. Life on the surface died out, but subsurface life continued.

2. The surface of Mars was never habitable, but the subsurface is a different matter (more moisture, less UV radiation). At some point in the history of Mars, fragments from a large space rock pierced the surface, and carried microbial spores directly into the habitable environment a few meters down.

Do I have proof that either of the two above stories is true? No, I do not.
If exploration of Mars continues, we'll eventually know. But not necessarily within five years.

Van Rijn
2012-Oct-08, 11:49 PM
Just as a reminder, the original discussion was about surface based Earth-like Martian life.


No, the original discussion was about lithopanspermia, not Martian life, surface Martian life, abundant Martian life, complex Martian life, Earth-like Martian life, still surviving Martian life, or Martian life so obvious even Curiosity could unambiguously identify it.

John Jaksich
2012-Oct-09, 12:17 AM
To ADIM:

Sorry to get back to you so late---I am citing a critic of Dr. David McKay--- his name is Dr. Michael Fuller, and he is a currently emeritus from U. C. Santa Barbara--and is at University of Hawaii, currently. I am somewhat unsure where I got the "Liquefaction quote" ---but I did read it some place ----> and I cannot currently find it :(

He is an expert on magnetism---> and has at least two publications on the ALH84001 meteorite.

Here are the listings:




Antretter, M., M. Fuller, Paleomagnetism and Rock Magnetism of Martian meteorite ALH84001, J. Phys. Chem. Earth, (A) Published on line, 2002.



Antretter, M. , M. Fuller, E. Scott, M. Jackson, B. Moskowitz, and P. Solheid, Paleomagnetic Record of Martian Meteorite ALH84001, JGR Planets, 108, E6, 5049, doi:10 1029/2002JE001979.*


He is very well versed in Rock magnetism.

Here is his vitae web site:

http://www.higp.hawaii.edu/~mfuller/MFpublications.html

Selfsim
2012-Oct-09, 12:40 AM
Just as a reminder, the original discussion was about surface based Earth-like Martian life.No, the original discussion was about lithopanspermia, not Martian life, surface Martian life, abundant Martian life, complex Martian life, Earth-like Martian life, still surviving Martian life, or Martian life so obvious even Curiosity could unambiguously identify it.Well thank you for taking my quoted words out of the context of the conversation from which they came. (You may want to have another read, to get the actual context).

This forum is the Life In Space forum, isn't it? What significance does lithopanspermia have in a Life in Space forum, if it isn't about life?

starcanuck64
2012-Oct-09, 07:31 PM
This seems like stacking one conjecture on another until you've got a "hypothesis" that seems to make a "conclusion".

If we're not even sure of the stellar environment that the young Sun and Earth were part of, what the general(not even exact) process of abiogenisis is, whether or not life can survive the launching, transit, and re-entry into a terrestrial environment where it can exploit the new conditions then what's the importance of saying that panspermia is possible?

A lot of things are possible, it's their probability that has significance. If you can point to a specific process taking place in a specific environment that we're confident existed not much less than 4 Billion years ago then you have something to work with, claiming panspermia is possible doesn't really seem to offer much in the way of an avenue to advance our understanding of the origins of life when we can't quantify its probability.

Colin Robinson
2012-Oct-09, 11:49 PM
This seems like stacking one conjecture on another until you've got a "hypothesis" that seems to make a "conclusion".

When you say "this seems", which particular "this" do you mean? Are you commenting on the material mentioned in the opening post of this thread, or on one or more of the later postings, or what? Or are you just making a general comment on what you see as "this" sort of thing?

Noclevername
2012-Oct-10, 12:01 AM
This forum is the Life In Space forum, isn't it? What significance does lithopanspermia have in a Life in Space forum, if it isn't about life?

Note that all the forms of life Van Rijn mentioned were Martian life. I don't believe that he ruled out life in general.

starcanuck64
2012-Oct-10, 12:14 AM
When you say "this seems", which particular "this" do you mean? Are you commenting on the material mentioned in the opening post of this thread, or on one or more of the later postings, or what? Or are you just making a general comment on what you see as "this" sort of thing?

All of it and I don't see stars being closer together in the early period of solar system formation being that much a leap forward in discovering the origins of life on Earth.

You still have to create these elaborate steps to get the alien life off the site of abiogenesis, transit to the target planet, enter safely and then survive, while indicating what's so different between the two sites that the same abiogenesis process couldn't have happened here.

While it's a possibility, does that have much relevance if it just has a tiny probability.

Noclevername
2012-Oct-10, 12:27 AM
You still have to create these elaborate steps to get the alien life off the site of abiogenesis, transit to the target planet, enter safely and then survive, while indicating what's so different between the two sites that the same abiogenesis process couldn't have happened here.
(Bold mine)

Just to nitpick: "Didn't" does not equal "couldn't have". In the scenario above, maybe the first site of abiogenesis was just first. If life was transferred from A to B, then any new life arising on B later would be out-competed by established A life.

starcanuck64
2012-Oct-10, 12:35 AM
(Bold mine)

Just to nitpick: "Didn't" does not equal "couldn't have". In the scenario above, maybe the first site of abiogenesis was just first. If life was transferred from A to B, then any new life arising on B later would be out-competed by established A life.

So it comes down to a matter of timing and the amount of material broadcast into space and the likelyhood of transit to a suitable system, whether or not the material will collide with the target site and whether or not the life carried on board will survive.

While it's possible, IMO you're still creating an almost unprovable hypothesis, when the much more likely explaination lies in a process that happened locally(on Earth).

We do have the one sample of Earth life to go by, if panspermia is at all viable there should be remnants of rocks blasted off the Earth's surface still in the solar system that contain fossil evidence of primitive life from around 3.8 billion ya.

Noclevername
2012-Oct-10, 12:38 AM
So it comes down to a matter of timing and the amount of material broadcast into space and the likelyhood of transit to a suitable system, whether or not the material will collide with the target site and whether or not the life carried on board will survive.

While it's possible, IMO you're still creating an almost unprovable hypothesis, when the much more likely explaination lies in a process that happened locally(on Earth).

I'm not creating a hypothesis, I was clarifying terminology (hence the "nitpick" warning label and the "in the scenario above"-- I didn't want anyone thinking it was my scenario). I personally think life on Earth started on Earth.

Selfsim
2012-Oct-10, 12:40 AM
Note that all the forms of life Van Rijn mentioned were Martian life. I don't believe that he ruled out life in general.There's a difference? Well that's news to me .. what exactly is that difference?

Noclevername
2012-Oct-10, 12:43 AM
There's a difference? Well that's news to me .. what exactly is that difference?

Er, life on Mars is only on Mars. Life in general is generally any life.

starcanuck64
2012-Oct-10, 12:47 AM
I'm not creating a hypothesis, I was clarifying terminology (hence the "nitpick" warning label and the "in the scenario above"-- I didn't want anyone thinking it was my scenario). I personally think life on Earth started on Earth.

I got that, I was just trying to clarify what I was trying to say, I think I'm having one of those days when it's hard to get my thoughts out clearly.

Noclevername
2012-Oct-10, 12:54 AM
I got that, I was just trying to clarify what I was trying to say, I think I'm having one of those days when it's hard to get my thoughts out clearly.

Ah, I have those days too. They end in a "Y".

eburacum45
2012-Oct-10, 03:48 AM
So it comes down to a matter of timing and the amount of material broadcast into space and the likelyhood of transit to a suitable system, whether or not the material will collide with the target site and whether or not the life carried on board will survive.

While it's possible, IMO you're still creating an almost unprovable hypothesis, when the much more likely explaination lies in a process that happened locally(on Earth). It could, in theory, be possible to determine whether any life found on Mars shares a common origin with life on Earth. Molecular analysis could not only tell if Mars life is related to Earth life, but also how long ago they diverged. Or molecular analysis could demonstrate that Mars life is entirely unrelated to Earth life, with a different genetic code, different proteins, and so on.


We do have the one sample of Earth life to go by, if panspermia is at all viable there should be remnants of rocks blasted off the Earth's surface still in the solar system that contain fossil evidence of primitive life from around 3.8 billion ya.A very good idea, and this is the sort of thing that is worth looking for. There might even be fossil life in space rocks blasted not only from Earth, but also from Mars, Europa, Enceladus, Ceres, Vesta, Titan and/or Venus...

Van Rijn
2012-Oct-10, 07:41 AM
Well thank you for taking my quoted words out of the context of the conversation from which they came. (You may want to have another read, to get the actual context).


I have read it, and I've reviewed it again. You claimed "Just as a reminder, the original discussion was about surface based Earth-like Martian life." But the original thread discussion was about the lithopanspermia hypothesis, which does not require Earth-based Martian life. What original discussion were you referring to?



This forum is the Life In Space forum, isn't it? What significance does lithopanspermia have in a Life in Space forum, if it isn't about life?

Of course it is about life. But that doesn't require it to be about life that Curiosity could identify, or for that matter, for it to be about any life on Mars at all.

Van Rijn
2012-Oct-10, 07:53 AM
Note that all the forms of life Van Rijn mentioned were Martian life. I don't believe that he ruled out life in general.

To clarify, I wasn't ruling out Martian life either. I was just pointing out that the original thread discussion was about lithopanspermia, not the much narrower subject of "surface based Earth-like Martian life" that Selfsim was arguing about.


Er, life on Mars is only on Mars. Life in general is generally any life.

Exactly.

Selfsim
2012-Oct-10, 10:40 AM
I have read it, and I've reviewed it again. You claimed "Just as a reminder, the original discussion was about surface based Earth-like Martian life." But the original thread discussion was about the lithopanspermia hypothesis, which does not require Earth-based Martian life. What original discussion were you referring to?Rather than recap the entire ~88 post thread, I'm going to attempt to 'cut to the chase' and guess that the main issue you're challenging me on, is the underlined part above. The rest of the matter began way back on post #6 where I asked:
Could the lithopanspermia mechanism be ruled out, if after say 5 years or so, no evidence of past life whatsoever, (fossilised), is found on Mars?It was probably this question which queried the relationship between life and lithopanspermia, given that 'Martian life' may/may not be concluded to have existed on Mars, after searching for signs for some extended arbitrary period of time, (I'll address this point below). Most subsequent posts raised all sorts of opinions and speculation to defend the idea that life may still be found on Mars, albeit, most likely now, (as the story goes), considerably underground, as opposed to surface dwelling. This seems to abandon the concept of lithopanspermic transmissable life, (or its precursors), having to be extremely hardy, (not to mention also abandoning current supporting arguments which are based on 'evidence' drawn from Earth-based extremophile/dormant biologies).



Of course it is about life. But that doesn't require it to be about life that Curiosity could identify, or for that matter, for it to be about any life on Mars at all.Ok .. so I'm about to plagiarise some well chosen words from Wiki/Lithopanspermia (http://en.wikipedia.org/wiki/Lithopanspermia), to explain where I was coming from (only for the sake of expediency ... I was unaware that these words existed prior to my post #6, by the way):

Even if life were to survive the hardships of space, or further, was being created in space, these would be very enduring life forms, as the theory itself proposes, and they would have already visibly populated and altered Venus and Mars as well as other moons in the solar system. Therefore, the absence of life in Venus, with a somewhat similar composition to Earth's primitive conditions or the absence of life on Mars, given the proposed "resilience" of life in space, damages the panspermia theory, at least based on observations of our own Solar System - the theory suggests that life would be more abundant in the Solar system.The absence of past life on Mars (or Venus) weakens the lithopanspermia hypothesis, and so there is thus some impact expected following some arbitrarily finite search period.
Frankly I don't care one way or the other about the outcomes of either exo-life or lithopanspermia speculations. I do see a lot of pirouetting going on, because of a lack of any useful, pertinent data supporting any of it.
The speculation is nothing more than story-telling, in the absence of any solid, relevant data ..

If anyone is suggesting in this discussion that the 'life' they are referring to is something other than organic carbon-based life, then I would say this would be utter fantasy-land stuff, which transcends scientific speculation, and is not even worthy of science-based consideration.

Noclevername
2012-Oct-10, 11:29 AM
If anyone is suggesting in this discussion that the 'life' they are referring to is something other than organic carbon-based life, then I would say this would be utter fantasy-land stuff, which transcends scientific speculation, and is not even worthy of science-based consideration.

Since we can't say what ET life would be like, we can't say what it isn't like, except where that possibility violates the laws of physics. Alternate biochemistries do not violate the laws of physics. Yes, real scientists do seriously study the possibility of such life. There are elements other than carbon that can form extremely complex molecules, though carbon is the best at doing so among the more common elements.

Also, something can be carbon-based and still be extremely different from Earth life. There are a lot of carbon compunds, we use only a relative handful. For example, there are hundreds of amino acids known, many of which can be found in some carbonaceous meteors, indicating that they can form readily under conditions common throughout space*. Even if organic compounds are the basic structure of such hypothetical life, the solvent fluid involved may not be water. For example, liquid methane has properties conducive to interactions of complex organics. Ammonia is common and also posesses many chemically appropriate qualities. As with carbon, liquid water is the most suitable that we know of, but it isn't the only contender.

Any life that may be out there will probably be based on carbon and water, simply because these things are so abundant in the universe. But closing our minds to other possibilities isn't scientific.

* Before you misinterpret, NO, I am not saying life can form in space.

Colin Robinson
2012-Oct-10, 11:39 AM
Rather than recap the entire ~88 post thread, I'm going to attempt to 'cut to the chase' and guess that the main issue you're challenging me on, is the underlined part above. The rest of the matter began way back on post #6 where I asked:It was probably this question which queried the relationship between life and lithopanspermia, given that 'Martian life' may/may not be concluded to have existed on Mars, after searching for signs for some extended arbitrary period of time, (I'll address this point below). Most subsequent posts raised all sorts of opinions and speculation to defend the idea that life may still be found on Mars, albeit, most likely now, (as the story goes), considerably underground, as opposed to surface dwelling. This seems to abandon the concept of lithopanspermic transmissable life, (or its precursors), having to be extremely hardy, (not to mention also abandoning current supporting arguments which are based on 'evidence' drawn from Earth-based extremophile/dormant biologies).

Interesting argument... but I think you are conflating two sorts of hardiness:

1. Ability to survive in a dormant state in challenging conditions (such as in a meteoroid travelling through interplanetary space).
2. Ability to metabolize and multiply in challenging conditions (such as on the surface of a planet with no surface moisture).

For meteoroid transfer to work, the organism concerned would of course need to be "hardy" in sense 1., but does that mean it would be "hardy" in sense 2.?


If anyone is suggesting in this discussion that the 'life' they are referring to is something other than organic carbon-based life, then I would say this would be utter fantasy-land stuff, which transcends scientific speculation, and is not even worthy of science-based consideration.

Well, I would not be so quick to rule out life-forms with a radically different chemistry...

BUT if we are talking about organisms spreading by meteoroid transfer between Earth and Mars (in either direction) or between Earth and Venus, then logically we are talking about life that is akin to Earth life, and therefore has a similar biochemistry.

And Earth life, (including extremophiles) does need moisture (liquid water) in order to metabolize and to multiply...

Paul Wally
2012-Oct-10, 02:38 PM
Sure, I think panspermia is possible, it's just a question of whether it is something that is very likely to happen anywhere. If Earth had life on it and Mars was habitable for a sufficiently long time, say a billion years, then life not being deposited on Mars during that habitable period must at least say something about the likelihood of such a transfer.

Well what exactly must it say about it (in terms of the broader generalised theory about exo-life, which you've mentioned in the past, which you say is feasible)?

Just to illustrate the principle: The implication would be that the frequency of panspermia events (or the probability of such events occurring during arbitrarily short time intervals) was sufficiently low as to not happen during the entire period when Mars was habitable. For instance, if panspermia was the kind of thing that could happen on average once every 10 000 years then it is very unlikely for there not to be any such events in say a billion years.

starcanuck64
2012-Oct-10, 05:45 PM
A very good idea, and this is the sort of thing that is worth looking for. There might even be fossil life in space rocks blasted not only from Earth, but also from Mars, Europa, Enceladus, Ceres, Vesta, Titan and/or Venus...

It would be nice to get a small fleet of long duration, semi-autonomous craft out looking around the solar system for this specific thing.

IsaacKuo
2012-Oct-10, 06:28 PM
It would be nice to get a small fleet of long duration, semi-autonomous craft out looking around the solar system for this specific thing.

I suspect it would be more cost effective to look for such blasted space rock fossils on the Moon. It has been acting as a flytrap for space rocks for billions of years. Unlike Earth, the Moon isn't a breeding ground for evidence contaminating microbes.

But before such a Moon probe, it would be worthwhile to try and find such fossil evidence here on Earth. There are some places on Earth which have luckily avoided geological destruction for billions of years, and the risk of Earth life contamination is counterbalanced by the much lower mission cost.

starcanuck64
2012-Oct-10, 06:38 PM
I suspect it would be more cost effective to look for such blasted space rock fossils on the Moon. It has been acting as a flytrap for space rocks for billions of years. Unlike Earth, the Moon isn't a breeding ground for evidence contaminating microbes.

But before such a Moon probe, it would be worthwhile to try and find such fossil evidence here on Earth. There are some places on Earth which have luckily avoided geological destruction for billions of years, and the risk of Earth life contamination is counterbalanced by the much lower mission cost.

That makes a lot of sense, maybe areas like the Canadian Shield would be a good place to look first.

Selfsim
2012-Oct-10, 09:30 PM
Interesting argument... but I think you are conflating two sorts of hardiness:

1. Ability to survive in a dormant state in challenging conditions (such as in a meteoroid travelling through interplanetary space).
2. Ability to metabolize and multiply in challenging conditions (such as on the surface of a planet with no surface moisture).1a. The trasferring lifeform doesn't necessarily have to be in the dormant state to survive the journey, if it finds itself surrounded by sufficient resources to survive for the duration of the transference.
2a. Some organisms have developed the ability to survive in a dehydrated state and also possess a demonstrated ability to survive the other conditions of transfer and the conditions upon arrival. Deinococcus radiodurans (http://en.wikipedia.org/wiki/Deinococcus_radiodurans) is one such organism.
Also, I think the term 'surface' is way too generalised. An ice ledge or shelf on the polar region of Mars may quite easily produce sufficient liquid water, repeatedly for finite times over a period of sufficient duration, for the right organism adapt to those conditions.
Once again, I'm not saying this particular variant could happen, but in the language of the professional speculator, its 'possible' .. (which in my view, is close to saying absolutely nothing of any merit, or scientific value, and should incur a heavy messaging board electron tax).
The point is that if the above rationale is adopted, (and it seems to have been in many speculator circles), then he/she who lives by the sword, should die by the sword (and nominate their own means of execution! :) )


For meteoroid transfer to work, the organism concerned would of course need to be "hardy" in sense 1., but does that mean it would be "hardy" in sense 2.?Adaption. The above mentioned organism has developed all the right characteristics to cater for all of it. Whether it had billions of years ago .. who knows? If it turns up on (or close to) the surface of Mars, then I'd say you'd have you're answer, (or more questions), right there!


Well, I would not be so quick to rule out life-forms with a radically different chemistry..If there's no test to test a hypothesis which expounds a non-carbon based lifeform, (and there isn't one because no-one knows how that lifeform could function so as to design a test for those functions), then the hypothesis is not testable, and therefore falls outside the scope of empirical science. It cannot be shown to be independently verifiable (nor falsifiable), and to the best of my knowledge, it has not yet been shown to even be theoretically possible, and can thus only be said to exist in waffly words, and wild imaginations.


BUT if we are talking about organisms spreading by meteoroid transfer between Earth and Mars (in either direction) or between Earth and Venus, then logically we are talking about life that is akin to Earth life, and therefore has a similar biochemistry.Yep … I wasn't the one who introduced the meaningless 'exotic' non-carbon based lifeforms into this discussion. I would have thought this fell outside the scope of litopanspermia. (And I think lithopanspermia itself, is considered within the scope of physical science - barely).


And Earth life, (including extremophiles) does need moisture (liquid water) in order to metabolize and to multiply…No problem if one considers the lifeform mentioned above.

Selfsim
2012-Oct-10, 11:39 PM
Since we can't say what ET life would be like, we can't say what it isn't like, except where that possibility violates the laws of physics. Alternate biochemistries do not violate the laws of physics. Yes, real scientists do seriously study the possibility of such life. There are elements other than carbon that can form extremely complex molecules, though carbon is the best at doing so among the more common elements.If a test cannot be designed to test for 'alternate' life chemistries, then the hypothesis which gives rise to them, (in the ontological sense), cannot be shown to be independently verifiable nor falsifiable, and thereby falls outside of the scope of the empirical side of the physical sciences. There are many theoretically possible things which are untestable .. In biological sciences, testability is crucial. This is what distinguishes biological sciences from say, physics (and this is because of the complexity which distinguishes life). We are talking life, which is defined by biological sciences. Empirical testing is where the crunch happens. If ya can't test it in biology … its a fantasy (eg: Homeopathy .. check out this list (http://en.wikipedia.org/wiki/List_of_branches_of_alternative_medicine) of treatments (mostly) excluded (or debunked) by biological science, on the basis of untestability, negative, or null test results!)

It seems frequently, this 'small', (yet unavoidable) fact, is persistently overlooked by sci-fi fans (and those who seek to develop an audience for it).


Also, something can be carbon-based and still be extremely different from Earth life. There are a lot of carbon compunds, we use only a relative handful. For example, there are hundreds of amino acids known, many of which can be found in some carbonaceous meteors, indicating that they can form readily under conditions common throughout space*. Even if organic compounds are the basic structure of such hypothetical life, the solvent fluid involved may not be water. For example, liquid methane has properties conducive to interactions of complex organics. Ammonia is common and also posesses many chemically appropriate qualities. As with carbon, liquid water is the most suitable that we know of, but it isn't the only contender.Can you demonstrate that any such organic solutes or solvents, when combined, result in the macro-functions accepted by mainstream biological sciences, as defining life?
If not, why should we discuss them in a life sciences context? Please demonstrate why. (Perhaps in a different thread, though).


Any life that may be out there will probably be based on carbon and water, simply because these things are so abundant in the universe. No .. AFAIK, the only life we know of, is based on carbon-based organic chemistry, involving a water based solvent. Thus far, I am not aware of any real-world discoveries, (or syntheses), which fall outside of this model.
The 'any life' you speculate about, is purely fictitious and cannot be shown to constitute life, (other than in word play and wild imaginings).


But closing our minds to other possibilities isn't scientific.Moreso is arguing something to be science based, which fails testability.


* Before you misinterpret, NO, I am not saying life can form in space.Why not?

I think perhaps a point worthwhile making is that the universal genetic code allows for many other theoretical permutations, which might code for amino acids. This is theory, is verifiable and falsifiable. Thus far, the universal genetic code defines all known life permutations. Nothing has ever been discovered which falls outside of this model, which is able to perform the basically accepted life functions. Until there is evidence of life beyond that defined by this model, scientific discipline demands a skeptical view of any theorised alternatives*.

Having said this, such speculation could be framed in a statement of scientific hypothesis, which could be testable. This would then at least be on the scientific process pathway.

*(Which on the basis of the available evidence, seems to be the opposite of what happens around these parts).

Selfsim
2012-Oct-10, 11:46 PM
Well what exactly must it say about it (in terms of the broader generalised theory about exo-life, which you've mentioned in the past, which you say is feasible)?Just to illustrate the principle: The implication would be that the frequency of panspermia events (or the probability of such events occurring during arbitrarily short time intervals) was sufficiently low as to not happen during the entire period when Mars was habitable. For instance, if panspermia was the kind of thing that could happen on average once every 10 000 years then it is very unlikely for there not to be any such events in say a billion years.Then you would be extrapolating from an instance case of one?!?

This would be an exteremely weak basis for developing a generalised theory!(??)

Noclevername
2012-Oct-11, 12:25 AM
The 'any life' you speculate about, is purely fictitious and cannot be shown to constitute life, (other than in word play and wild imaginings).

You seem to have a hard time differentiating thought-experiments or rational speculation from "word play and wild imaginings".

If you don't understand how important that distinction is, I think this is no longer a fruitful discussion.

eburacum45
2012-Oct-11, 03:24 AM
I think perhaps a point worthwhile making is that the universal genetic code allows for many other theoretical permutations, which might code for amino acids. This is theory, is verifiable and falsifiable. Thus far, the universal genetic code defines all known life permutations. Nothing has ever been discovered which falls outside of this model, which is able to perform the basically accepted life functions. Until there is evidence of life beyond that defined by this model, scientific discipline demands a skeptical view of any theorised alternatives*.

The universal genetic code that occurs on Earth is linked through evolution to a last universal common ancestor (LUCA).
http://en.wikipedia.org/wiki/Last_universal_ancestor
If we discovered life on Mars, Europa or elsewhere which also could be shown to be linked to this last universal common ancestor, that would be good evidence for localised panspermia. If, on the other hand, there was no such relationship, then we could probably rule panspermia out and hypothesise that separate abiogenesis events had occured.

There is, I suppose, a slight possibility that the result of a separate abiogenesis event would produce organisms which appear to have descended from a last common ancestor with Earth life, but that seems very unlikely to me. Other views might vary on this matter

Selfsim
2012-Oct-11, 06:22 AM
The universal genetic code that occurs on Earth is linked through evolution to a last universal common ancestor (LUCA).
http://en.wikipedia.org/wiki/Last_universal_ancestor
If we discovered life on Mars, Europa or elsewhere which also could be shown to be linked to this last universal common ancestor, that would be good evidence for localised panspermia. If, on the other hand, there was no such relationship, then we could probably rule panspermia out and hypothesise that separate abiogenesis events had occured.

There is, I suppose, a slight possibility that the result of a separate abiogenesis event would produce organisms which appear to have descended from a last common ancestor with Earth life, but that seems very unlikely to me. Other views might vary on this matterHmm … well, the universal genetic code is cited as just one of the evidences supporting the LUCA theory. There are also many other lines of evidence used in support of it as well. Such as, for example: phylogenic trees, anatomical vestiges, statistical phylogeny, parahomology, morphological commonalities, etc.
I think one critical underlying assumption behind the LUCA theory, is that Earth is assumed to be a thermodynamically isolated system (as far as matter transfer is concerned). Clearly panspermia challenges, or even negates that assumption. So, I'm not sure if anything following on from such an assumption, could be taken in reverse as necessarily inferring anything anything about panspermia(??) It could quite easily be seen as a chalk-and-cheese comparison, depending on the details of the hypothetical scenario.

A lot would depend on the nature of such a discovery if found on a local planet/moon/asteroid etc, which shares the same degree of localised thermodynamic isolation as Earth. This is another point worthy of making here .. following where the data takes us, in my view, is essential and yet, is often overlooked by eagerness to play around with philosophically based logic discussions which don't resolve anything much in this area. *

And at present, we have zero relevant data. As such, I'd have to say that frankly, I haven't a clue as to what one could conclude from such a hypothetical. It depends entirely on the other detailed aspects of such a discovery.
For instance, that an alien lifeform might somehow, have ended up emerging from amino acids, would be a good starting point for a line of enquiry. Are they the same bases as our version of life uses? If not, where did they come from? Perhaps when they turned up in a given environment, is as critical as how the chemistry evolved from thereon(??) We have absolutely no idea about any of this, nor can we even synthesise any models which have any semblance of precedent, in terms of resulting in life functions! We can't 'postdict' the initial conditions in sufficient detail, to give any assurances about our own life, let alone another one!



* Even though I may stand accused of: 'having a hard time differentiating thought-experiments, or rational speculation from "word play and wild imaginings" '… I can assure all, that without the discipline (and hack-work involved) in defining the detailed assumptions of real scientific speculation, it becomes easy to partake in what invariably becomes speculative chit-chat. I personally find exercising discipline to be a challenge, and is a quite a distinguishing feature of real scence. It mightn't be as much 'fun', but I find it leads to much greater insights into physical reality, which are frequently counterintuitive and hence, it has its own unique set of payoffs.

Colin Robinson
2012-Oct-11, 07:56 AM
Some organisms have developed the ability to survive in a dehydrated state and also possess a demonstrated ability to survive the other conditions of transfer and the conditions upon arrival. Deinococcus radiodurans (http://en.wikipedia.org/wiki/Deinococcus_radiodurans) is one such organism.
If there's no test to test a hypothesis which expounds a non-carbon based lifeform, (and there isn't one because no-one knows how that lifeform could function so as to design a test for those functions), then the hypothesis is not testable, and therefore falls outside the scope of empirical science. It cannot be shown to be independently verifiable (nor falsifiable), and to the best of my knowledge, it has not yet been shown to even be theoretically possible, and can thus only be said to exist in waffly words, and wild imaginations.

Yep … I wasn't the one who introduced the meaningless 'exotic' non-carbon based lifeforms into this discussion. I would have thought this fell outside the scope of litopanspermia. (And I think lithopanspermia itself, is considered within the scope of physical science - barely).


And Earth life, (including extremophiles) does need moisture (liquid water) in order to metabolize and to multiply...

No problem if one considers the lifeform mentioned above.

Deinococcus radiodurans is noted for its ability to repair DNA damage by radiation and desiccation (drying out).

But is it able to perform its metabolism without liquid water in its cytoplasm? If the answer is "yes", how does it accomplish the feat?

Metabolism is a chemical process, which earthling organisms commonly perform using an aqueous (liquid-water based) solution. Metabolic chemistries which do not involve liquid water are indeed conceivable (e.g. in liquid hydrocarbon as on Titan), but they would be distinctly exotic, even if carbon-based. (A metabolic chemistry with no liquid of any sort would be even more exotic.)

But you seem to be saying that there would be no need to go to Titan to find an organism so exotic that it doesn't need liquid H20 for its metabolism, because it is right here on Earth in the form of Deinococcus radiodurans??

Selfsim
2012-Oct-11, 10:24 AM
...
... But you seem to be saying that there would be no need to go to Titan to find an organism so exotic that it doesn't need liquid H20 for its metabolism, because it is right here on Earth in the form of Deinococcus radiodurans??Er .. no .. how did going to Titan to look for 'exotic life' come into this?
I was merely pointing out that D. radiodurans has achieved hardiness by a couple of different 'standards', ie: radiation and desiccation resistance, via the same adapted mechanism (DNA repair). It still requires water, as does every other Earth-based lifeform .. why wouldn't water be capable of being transported along with it, during a panspermia event? (There's also water on Mars for its continued survival, too ... which could also be liquid for long enough to rehydrate the organism ...)

eburacum45
2012-Oct-11, 10:29 PM
Hmm … well, the universal genetic code is cited as just one of the evidences supporting the LUCA theory. There are also many other lines of evidence used in support of it as well. Such as, for example: phylogenic trees, anatomical vestiges, statistical phylogeny, parahomology, morphological commonalities, etc.
I think one critical underlying assumption behind the LUCA theory, is that Earth is assumed to be a thermodynamically isolated system (as far as matter transfer is concerned). Clearly panspermia challenges, or even negates that assumption. So, I'm not sure if anything following on from such an assumption, could be taken in reverse as necessarily inferring anything anything about panspermia(??) It could quite easily be seen as a chalk-and-cheese comparison, depending on the details of the hypothetical scenario.

A lot would depend on the nature of such a discovery if found on a local planet/moon/asteroid etc, which shares the same degree of localised thermodynamic isolation as Earth. This is another point worthy of making here .. following where the data takes us, in my view, is essential and yet, is often overlooked by eagerness to play around with philosophically based logic discussions which don't resolve anything much in this area.
You have hit the nail on the head; if life were found on a local planet etc, we could examine it using the same criteria which apply in the LUCA theory, and if it is evidently related to the common ancestor, then we can use that as good confirmation of local panspermia; if not, then the opposite applies.

The universal code is only one of 1.5 x 10e84 different possible genetic codes, but probably less than one in a million of those codes are as optimal as the one we use. That still leaves around 10e78 different, optimal codes that might occur on another planet with a separate abiogenesis event. If we ever find life in the solar system we should be able to easily discriminate between a situation where panspermia has occurred and one where it has not. However this discovery would have very little relevance to interstellar panspermia.

Colin Robinson
2012-Oct-11, 11:28 PM
Er .. no .. how did going to Titan to look for 'exotic life' come into this?
I was merely pointing out that D. radiodurans has achieved hardiness by a couple of different 'standards', ie: radiation and desiccation resistance, via the same adapted mechanism (DNA repair). It still requires water, as does every other Earth-based lifeform .. why wouldn't water be capable of being transported along with it, during a panspermia event? (There's also water on Mars for its continued survival, too ... which could also be liquid for long enough to rehydrate the organism ...)

You are asking me why an organism like Deinococcus r. couldn't have spread from Earth to Mars via lithopanspermia? My answer is that I know of no reason at all why it couldn't...

But given that these extremophiles do require liquid water, where would we logically expect to find their descendants on Mars today?

Would we expect to find them growing and metabolizing abundantly all over the Martian surface?

Or would we expect to find them only in the comparatively rare environments where (if anywhere) liquid water exists, e.g. in underground aquifers, or niche environments at the poles?

Selfsim
2012-Oct-12, 01:24 AM
You have hit the nail on the head; if life were found on a local planet etc, Well for starters, the tests applied which might lead to a conclusion of 'life detected', necessarily assume our model of life in the first place (and your assumptions exclude the 'possibility' of a false positive result, or an unwittingly inappropriately designed test).


we could examine it using the same criteria which apply in the LUCA theory, In the light of no prior exo-specimen data, at the moment, I don't really see how else we could analyse such a finding … but that doesn't mean that there isn't an alternate way. :)
and if it is evidently related to the common ancestor,But this is the crux of the issue … exactly how that conclusion is formed, is as much a function of the nature of the find, as it is a function of the nature of the tests, and the assumptions made in the model … a change in any of which, could easily lead along a completely distinct investigative pathway, and conclusion.
…. then we can use that as good confirmation of local panspermia; if not, then the opposite applies.Well, what do you want me to say? From my perspective, you have assumed a huge amount prior to this conclusion .. some might even say, 'astronomical in proportion'!
(Some may not, however) :)


The universal code is only one of 1.5 x 10e84 different possible genetic codes, but probably less than one in a million of those codes are as optimal as the one we use. How do you estimate this probability?
That still leaves around 10e78 different, optimal codes that might occur on another planet with a separate abiogenesis event. Why would one assume that any code combinations other than our own, might result in any life at all? .. And why are we now speaking quantitatively, when the numbers you cite, have zero basis of validity in physical evidence?
If we ever find life in the solar system we should be able to easily discriminate between a situation where panspermia has occurred and one where it has not.If I follow the logic of your argument, I would be likely to come to the same conclusion. But there is no substance behind the scenario you portray. Logic won't solve the problem, when the assumptions made are totally synthesised, and without support.
However this discovery would have very little relevance to interstellar panspermia... A whole bunch more of synthesised assumptions yet again?


My point is as before … it depends almost entirely on the nature of 'the find'.

And that's about all which can be rationally said about the matter, at this stage of our knowledge development!

Colin Robinson
2012-Oct-12, 05:44 AM
Hmm … well, the universal genetic code is cited as just one of the evidences supporting the LUCA theory. There are also many other lines of evidence used in support of it as well. Such as, for example: phylogenic trees, anatomical vestiges, statistical phylogeny, parahomology, morphological commonalities, etc.
I think one critical underlying assumption behind the LUCA theory, is that Earth is assumed to be a thermodynamically isolated system (as far as matter transfer is concerned).

This is an extraordinary statement!

Even ignoring your misuse of a key scientific term like "thermodynamically"...

The notion of an LUCA is undoubtedly consistent with the notion that Earth has been biologically isolated for billions of years.

But you say that isolation is a "critical underlying assumption"... Isn't this logically equivalent to saying that scientists have concluded that all Earth life has a single beginning, only because they assumed that a second beginning was out of the question?

That without such an assumption, the lines of evidence you've mentioned, (universal genetic code, anatomical vestiges etc) would not be enough to make the case for a LUCA?

If so, then the whole scientific argument for a LUCA would be a circular argument...

Is this really what you're saying here, Selfsim?


I personally find exercising discipline to be a challenge, and is a quite a distinguishing feature of real scence.

Then please try to exercise a little discipline in how you use terms like "critical underlying assumption"...

eburacum45
2012-Oct-12, 08:13 AM
Well for starters, the tests applied which might lead to a conclusion of 'life detected', necessarily assume our model of life in the first place (and your assumptions exclude the 'possibility' of a false positive result, or an unwittingly inappropriately designed test). My only assumption is that we will one day be in a position to determine if there is life on other bodies in the Solar System. I assume that this will be done by sample-and-return missions, or even by manned missions. Hopefully there won't be too much risk of a false positive from such missions; but contamination by previous missions from Earth could pose such a risk, and we may not be able to eliminate false positives of that kind.


From my perspective, you have assumed a huge amount prior to this conclusion .. some might even say, 'astronomical in proportion'!
My only assumptions are laid out above; if you are aware of any others I may have made but I'm not aware of, please let me know.


How do you estimate this probability? That estimate is not mine; according to Wikipedia (http://en.wikipedia.org/wiki/Genetic_code#Origin) it comes from Michael Yarus' Life from an RNA World: The Ancestor Within .
The estimate for optimality comes from here
http://www.ncbi.nlm.nih.gov/pubmed/9732450
I suspect that the estimate for optimality might be itself optimistic, but I would be very surprised if it were 78 orders of magnitude wrong.

Note that we know for sure that the current 'universal genetic code' is not the only possible code, because it is not universal; it has mutated many times over the years, to give at least 18 different variants on this planet alone.
http://en.wikipedia.org/wiki/List_of_genetic_codes

By analysing any alien microbe at a genetic level we should be able to detect if its particular variant of the genetic code is also evolved from a common ancestor, or if it comes from one of the 100,000,000,000,000,000,000,000,000,000,000,000,00 0,000,000,000,000,000,000,000,000,000,000,000,000, 000,000,000,000 other possibilities.

Paul Wally
2012-Oct-12, 03:13 PM
Then you would be extrapolating from an instance case of one?!?

This would be an exteremely weak basis for developing a generalised theory!(??)

I was only talking about panspermia on Mars and not extrapolating beyond that case. Also, I don't see the relevance of panspermia to a general theory of abiogenesis, which is what I was referring to in earlier discussions.

Selfsim
2012-Oct-13, 06:00 AM
This is an extraordinary statement!

Even ignoring your misuse of a key scientific term like "thermodynamically"…Admittedly, a somewhat rushed post, mixing two different concepts I had in mind .. 'thermodynamically closed', and 'biologically isolated' (which somehow ended up as: 'thermodynamically isolated') however, what I wrote in brackets, qualified what I meant ..

Earth is assumed to be a thermodynamically isolated system (as far as matter transfer is concerned)Another way of saying this is that Earth and its life, has in the past, been modelled as a thermodynamically closed system .. (this has changed in more recent times, however). I'm Ok with 'Biologically isolated' too, if you prefer that …


But you say that isolation is a "critical underlying assumption"... Isn't this logically equivalent to saying that scientists have concluded that all Earth life has a single beginning, only because they assumed that a second beginning was out of the question?Actually, in retrospect, I think I may have been off the mark about this (for reasons other than what you imply). After thinking about this some more, and reviewing some of the analysis behind LUCA , I can't find anything in particular, which would necessarily require Earth to be isolated. It may be taken (by some) to infer it, but I can't see anything which would explicitly rule out initial external delivery via panspermia as well. (The rate of delivery might alter things somewhat .. but it may not, also).

As such, I'll withdraw my speculative query:
I think one critical underlying assumption behind the LUCA theory, is that Earth is assumed to be a thermodynamically isolated system (as far as matter transfer is concerned).(Note that this was intended more as a query than an assertion, also).

The point I'm trying to make, about LUCA commonality being used as evidence of panspermia .. would still however depend on the nature of the finding, specifically, the morphologies, genetic model, mechanisms, chemistry, etc and the similarity or otherwise, with the LUCA life interpretive model. Until that time, my view is that panspermia and LUCA hypotheses, should be seen as addressing two separate issues. I doubt that the degree of 'relatedness' would be a cut and dried matter, (even if a common panspermia event was involved in the origin) .. it may be moreso in Earth-life ancestry tracing .. because of the abdundant other supporting species, geological, environmental and evolutionary data (which constrain the conclusions) .. but what if the exo-life species is extraordinarily rare in its own native environment or it doesn't necessarily exhibit the same evolutionary measures as Earth-like life (eg: mutation rates, horizontal transfers, etc)? How would one differentiate whether certain similar characteristics had their origins native to that environment, or came from elsewhere, if they were similar to our LUCA's? Why assume a second abiogenesis would necessarily result in dissimilarities from our LUCA? (Ie: just because the theoretical permutation space in the genetic code might be large*, doesn't mean that there may not be an affinity for a certain code preference .. we just don't know ..) (Note: I'm also not making any particular claims one way or the other here, either).

It should also not be forgotten that the idea of the existence of similar exo-life in the first place, is a pure assumption, as well.


Then please try to exercise a little discipline in how you use terms like "critical underlying assumption"...Fair enough … (chuckle ... chuckle ….)
Request granted!

*I'll address the big numbers issue in a separate post ..

Colin Robinson
2012-Oct-13, 10:18 PM
Admittedly, a somewhat rushed post, mixing two different concepts I had in mind .. 'thermodynamically closed', and 'biologically isolated' (which somehow ended up as: 'thermodynamically isolated') however, what I wrote in brackets, qualified what I meant ..
Another way of saying this is that Earth and its life, has in the past, been modelled as a thermodynamically closed system .. (this has changed in more recent times, however). I'm Ok with 'Biologically isolated' too, if you prefer that …

I appreciate the thought you've given to the points I raised.

I do prefer the expression "biologically isolated" to "thermodynamically closed system" in this context. My reason is that "thermodynamics" is about the dynamics of energy, especially heat energy. As long as light and heat have been reaching Earth from the Sun, Earth has not been a thermodynamically closed system.




I doubt that the degree of 'relatedness' would be a cut and dried matter, (even if a common panspermia event was involved in the origin) .. it may be moreso in Earth-life ancestry tracing .. because of the abdundant other supporting species, geological, environmental and evolutionary data (which constrain the conclusions) .. but what if the exo-life species is extraordinarily rare in its own native environment or it doesn't necessarily exhibit the same evolutionary measures as Earth-like life (eg: mutation rates, horizontal transfers, etc)? How would one differentiate whether certain similar characteristics had their origins native to that environment, or came from elsewhere, if they were similar to our LUCA's? Why assume a second abiogenesis would necessarily result in dissimilarities from our LUCA? (Ie: just because the theoretical permutation space in the genetic code might be large*, doesn't mean that there may not be an affinity for a certain code preference .. we just don't know ..) (Note: I'm also not making any particular claims one way or the other here, either).

I would agree that the degree of "relatedness" of organisms found on different planets might not be a cut and dried matter. E.g. if microbes are found on Mars, with biochemical and morphological similarities as well as differences compared to Earth microbes, it could prove hard to establish whether they were directly related (due to lithopanspermia) or unrelated (due to an independent abiogenesis).

It would be comparable in a way to CERN's discovery of a new sub-atomic particle earlier this year. The particle had characteristics expected for the till-then-hypothetical Higgs boson, but whether it was in fact a Higgs boson was far from cut-and-dried. As this example shows, verification or falsification of a scientific conjecture is not necessarily a single sudden event...

That doesn't mean that scientific conjectures are immune from verification and falsification, just that it takes time, effort and considerable patience...

Selfsim
2012-Oct-13, 11:58 PM
I appreciate the thought you've given to the points I raised.No problem … I do use these conversations as motivation to do heaps more reading on these topics … if I've got something wrong, then feel free to explain why, (or use references … I do read the ones you have posted on other topics, by the way …)


I do prefer the expression "biologically isolated" to "thermodynamically closed system" in this context. My reason is that "thermodynamics" is about the dynamics of energy, especially heat energy. As long as light and heat have been reaching Earth from the Sun, Earth has not been a thermodynamically closed system.Err … in thermodynamics, a closed system (http://en.wikipedia.org/wiki/Closed_system#In_thermodynamics) is one which can exchange energy with its surroundings, (as heat or work), but not matter … an isolated system can do neither.
During the Boltzmann and Shrodinger era, IIRC, thinking along the lines of thermodynamics, (as a way of modelling life), was guided by the closed system model, (life exchanges heat and work with its surroundings, but not matter (during steady-state functioning)). Whilst this might be a separate matter from looking at Earth as a system in the universe, there wasn't a lot of evidence that infalling asteroids might carry life pre-cursors then either. Evolution was also a big influence in scientific thinking back in those days, too. I think panspermia, whilst certainly being around in those days as an idea, was not favoured due to this lack of seemingly relevant evidence from asteroid analysis, and the influence of Evolutionary thinking. Now that the evidence is materialising in more modern times, the idea is more 'acceptable'. The thinking about Earth being, (somewhat crudely), modelled as a closed system during that era, would also impact thinking about how life might have arisen. Clearly if it is viewed as a closed system, then panspermia would be inconsistent with this paradigm.


I would agree that the degree of "relatedness" of organisms found on different planets might not be a cut and dried matter. E.g. if microbes are found on Mars, with biochemical and morphological similarities as well as differences compared to Earth microbes, it could prove hard to establish whether they were directly related (due to lithopanspermia) or unrelated (due to an independent abiogenesis).I'm not convinced that the numbers cited by eburacum can be taken as evidence that a similar version of genetic code, if discovered, would necessarily imply a common LUCA (or the opposite). The figure cited, is about the information modelling perspective, and has to do with resilience to noise in the channel. This is a secondary matter which influences accurate replication from the genetic code/'blueprint'. Whilst it may influence replication, and therefore longevity of an organism's existence, I don't see it should be necessarily taken as being indicative of relatedness.

Its a numbers game again .. typically used to win an argument, which is a different matter from addressing the fundamental issue. (Not that I'm accusing eburacum of consciously trying to doing this, the argument is frequently found in reading materials on panspermia).


It would be comparable in a way to CERN's discovery of a new sub-atomic particle earlier this year. The particle had characteristics expected for the till-then-hypothetical Higgs boson, but whether it was in fact a Higgs boson was far from cut-and-dried. As this example shows, verification or falsification of a scientific conjecture is not necessarily a single sudden event… I don't agree that it would be comparable. The complexity of life models goes way, way beyond any complexity (if at all) in the Standard Particle Model.
Chalk and cheese again, if you ask me .. and there's way more theoretical and empirical supporting evidence with the Standard Particle Model .. it can actually make valid predictions! No life model can do this, with the backing of prior empirical evidence. There are repeatable tests which when applied, will answer the questions about the particle finding … not necessarily so, for hypothesised non-Earth 'life'.

Colin Robinson
2012-Oct-14, 01:50 AM
No problem … I do use these conversations as motivation to do heaps more reading on these topics … if I've got something wrong, then feel free to explain why, (or use references … I do read the ones you have posted on other topics, by the way …)

That's encouraging to know.


Err … in thermodynamics, a closed system (http://en.wikipedia.org/wiki/Closed_system#In_thermodynamics) is one which can exchange energy with its surroundings, (as heat or work), but not matter … an isolated system can do neither.

OK. sorry.

Judging by the WP page you've referred to, I was confusing the meaning of "closed system" in thermodynamics with what "closed system" means in classical mechanics...


During the Boltzmann and Shrodinger era, IIRC, thinking along the lines of thermodynamics, (as a way of modelling life), was guided by the closed system model, (life exchanges heat and work with its surroundings, but not matter (during steady-state functioning)). Whilst this might be a separate matter from looking at Earth as a system in the universe, there wasn't a lot of evidence that infalling asteroids might carry life pre-cursors then either. Evolution was also a big influence in scientific thinking back in those days, too. I think panspermia, whilst certainly being around in those days as an idea, was not favoured due to this lack of seemingly relevant evidence from asteroid analysis, and the influence of Evolutionary thinking. Now that the evidence is materialising in more modern times, the idea is more 'acceptable'. The thinking about Earth being, (somewhat crudely), modelled as a closed system during that era, would also impact thinking about how life might have arisen. Clearly if it is viewed as a closed system, then panspermia would be inconsistent with this paradigm.

I'm not convinced that the numbers cited by eburacum can be taken as evidence that a similar version of genetic code, if discovered, would necessarily imply a common LUCA (or the opposite).

Are you convinced that all known life-forms here on Earth are in fact related?

In other words, do you think that

1. the scientists who've reached that conclusion, have done so on the basis of sufficient evidence (including genetics, morphology etc)?

2. Or did they reach the LUCA conclusion just because of the assumptions they made: e.g. because they assumed that one abiogenesis was more likely than more than one, and that arrival of life from space was not at all likely?

If your answer to question 1. is "yes"... then would it not be possible, in principle, eventually to study the genetics, morphology etc of any martian biota, and reach a conclusion about whether or not the martian biota, too, share a LUCA with terrestrial life?

Or, if your answer to question 2. is "yes"... doesn't a lot of mainstream science go out the window, as a set of unsafe conclusions drawn from a circular argument?

Selfsim
2012-Oct-14, 04:46 AM
My only assumption is that we will one day be in a position to determine if there is life on other bodies in the Solar System. I assume that this will be done by sample-and-return missions, or even by manned missions. Hopefully there won't be too much risk of a false positive from such missions; but contamination by previous missions from Earth could pose such a risk, and we may not be able to eliminate false positives of that kind.Where I'm coming from is that we search by necessity for another instance of carbon-based, 'Earth-like' life. This 'choice' automatically excludes a myriad of other non-evidence based speculative 'possibilities', in a mind-boggling search space, whose occurrence might be said to be just as 'likely', (in frequency), as the possibility that carbon-based Earth-like life exists elsewhere. We develop a test for our version of life. For me, the only reason that the 'exo-life' hypothesis might be valid is because we can test for Earth-like life. If the test doesn't exist, then its not a testable hypothesis … its just an idea. (That the test can't be practically applied throughout the observable universe, also makes the testing of this hypothesis, practically infeasible). None-the-less, we then arbitrarily narrow the 'possibility space' even more, by looking for a very specific environment, in which a very particular 'optimal variant', seems to exist, (ie: Earth-like-conditions), although we have no idea of exactly what sensitivity other 'possible' lifeforms may have to those conditions, nor do we have any idea of what the sensitivity of the chemical pre-cursors were, to their original life-emerging environment. The bases of attraction for other than the Earth life code, (or the majority of all other theoretical genetic code variants), in terms of giving rise to 'life' signs, is also unknown, so consideration of the size of the theoretical 'optimal' possibility space, is a meaningless exercise.

Just how narrow and specific is this search criteria, in the face of the huge plethora of possibilities? Why should we assume that directed searches for this specific target would have any better chance of finding it, than a pure chance discovery, brought on by the mere act of exploration?

That we can convince ourselves that our miniscule understanding of life, has any chance of improving upon a chance discovery via directed searches, seems absurd to me.

And then we draw inferences from hypothesised life speculated to match/not match our own very specific model, in order to rule out other speculations, which may just as well be said to have no real data-based equivalent, anyway?


My only assumptions are laid out above; if you are aware of any others I may have made but I'm not aware of, please let me know. Well, for starters, there are many assumptions laid out in the references for the information channel hypothesis you provided.
The author makes it clear that there are 'several assumptions which reflect the lack of experimental knowledge about the environment where the code emerged'. I'm sure there are others but I don't have the time to review the entire field!
These assumptions make things much less certain and more speculative, even in the face of attempts at drawing inference from statistical quantification of a secondarily related topic (see below).


That estimate is not mine; according to Wikipedia (http://en.wikipedia.org/wiki/Genetic_code#Origin) it comes from Michael Yarus' Life from an RNA World: The Ancestor Within .
The estimate for optimality comes from here
http://www.ncbi.nlm.nih.gov/pubmed/9732450
I suspect that the estimate for optimality might be itself optimistic, but I would be very surprised if it were 78 orders of magnitude wrong.

Note that we know for sure that the current 'universal genetic code' is not the only possible code, because it is not universal; it has mutated many times over the years, to give at least 18 different variants on this planet alone.
http://en.wikipedia.org/wiki/List_of_genetic_codes

By analysing any alien microbe at a genetic level we should be able to detect if its particular variant of the genetic code is also evolved from a common ancestor, or if it comes from one of the 100,000,000,000,000,000,000,000,000,000,000,000,00 0,000,000,000,000,000,000,000,000,000,000,000,000, 000,000,000,000 other possibilities.… The numbers game …?..
The one in a million 'optimal code' statistic comes from an analogous theoretical model, conceived to provide some means of explaining the accuracy of protein synthesis from genetic instructions. The code itself can correct for translation errors due to usage of a triplet sequence. The specificivity of this schema when compared with the theoretical possibility space suggests that the code evolved to satisfy competing constraints, which is assumed might curtail its own development, (presuming that the eventual outcome was selected naturally). The author also suggests that this infers a single original source.

So, who says the information schema itself would exist somewhere else? Why should it? We have no idea about what a universally generalised life model might be. Our genetic code is ours and that's all we know. Why would the constraints (the need for diverse amino-acids, error-tolerance and minimal cost of resources), necessarily be relevant in another hypothesised emergence environment? The list of ramifications originating from this speculative assumption could go on forever .. and they seem to have been erased from consideration and glossed over as being trivial .. why should they be? Why not assume, infer, suggest, presume nothing? What value does all this assuming, inferring, presuming represent in reality?

Just 'checking out' the scene on another local planet should suffice .. anything else affordable would also be nice ... but not compulsory.

Selfsim
2012-Oct-14, 05:18 AM
Are you convinced that all known life-forms here on Earth are in fact related?I don't have to be convinced. Others seem to think they do.


In other words, do you think that

1. the scientists who've reached that conclusion, have done so on the basis of sufficient evidence (including genetics, morphology etc)? I have no problems with the reasoning. The problem is, that applying the same reasoning for the purposes of inferring something about a non-Earth-based fictitious exo-life model, at the moment, represents about as much value, as the fictitious exo-life model does … aka … zip!


2. Or did they reach the LUCA conclusion just because of the assumptions they made: e.g. because they assumed that one abiogenesis was more likely than more than one, and that arrival of life from space was not at all likely?Did they ever assume any of this?
I would suggest that the LUCA hypothesis was formed on the basis of the available evidence (and careful application of the scientific process throughout the analysis of it).


If your answer to question 1. is "yes"... then would it not be possible, in principle, eventually to study the genetics, morphology etc of any martian biota, and reach a conclusion about whether or not the martian biota, too, share a LUCA with terrestrial life?Studying any morphology which we may be lucky enough to discover would surely be possible! Using the LUCA methodology would be unavoidable, (because we presently know no other way), but we may also find out very quickly, that particular methodology was as dependent on the morphology and genetic models developed directly from experimentation and observations of Earth-life.

Who knows what method would emerge from analysis of an unknown discovery?

Colin Robinson
2012-Oct-14, 06:18 AM
The list of ramifications originating from this speculative assumption could go on forever .. and they seem to have been erased from consideration and glossed over as being trivial .. why should they be? Why not assume, infer, suggest, presume nothing? What value does all this assuming, inferring, presuming represent in reality?.

Definitions of the word assume (http://www.thefreedictionary.com/assume) include "take for granted, suppose".

I'd agree that taking stuff for granted can be dangerous in science. It is another thing to suppose something to be true in the sense of entertaining an idea for the sake of finding out its implications. As Karl Popper says, science is about conjectures and refutations...

Without a conjecture like meteoroid transfer, scientists would have taken for granted that any microbial life on Mars is unrelated to Earth life, (unless it's an obvious import from a recent space probe).

Thanks to the meteoroid transfer conjecture, they won't take for granted that martian life is either related or unrelated — they'll have both conjectures in mind, and try to falsify one or the other.

eburacum45
2012-Oct-14, 07:14 AM
Please don't think I'm trying to win an argument; I'm really enjoying Selfsim's detailed analysis of the possibilities. I absolutely agree that we should avoid making any assumptions, but that doesn't mean we cannot consider the options methodically.

I see the question as a set of options, which will (hopefully) be narrowed down if and when we find more data.
If we don't find life in the Solar System, the options are
1.1/ there is none
1.2/There is some, but we haven't looked hard enough
1.2a/ there is some, but it is undetectable to our science because of unknown factors (it might be hiding, or otherwise impossible to detect).

If we find do life in the Solar System outside Earth, we would need to examine whether is is related to Earth life. The options are;
2.1/it shares the same biochemistry and genetic code as Earth life
2.2/it has a slightly different biochemistry amd slightly different genetic code to Earth life
2.3/ it has a slightly different biochemistry and a radically different genetic code from Earth life (one of the 10e78 variants mentioned in earlier posts)
2.4/ it has radically different biochemistry and a radically different genetic code (or possibly no such code).
Note that accidental contamination by space probes could prodce a false positive, but this would fall under option one (unless it mutates really rapidly to live on the surface on another world)

Even if we don't find life elsewhere in the solar system that doesn't mean that life is absent from the rest of the universe. One day, perhaps, we will be able to send probes or manned missions to other stars to find if there us life there.

If we find life in other planetary systems then the same four options apply;
3.1/ it shares the same biochemistry and genetic code as Earth life
3.2/ it has a slightly different biochemistry amd slightly different genetic code to Earth life
3.3/ it has a slightly different biochemistry and a radically different genetic code from Earth life (one of the 10e78 variants mentioned in earlier posts)
3.4/ it has radically different biochemistry and a radically different genetic code (or possibly no such code).

Now it is entirely possible that the life found within the solar system will be radically different to life found outside the solar system; in fact that seems to be very likely to me. If we find that life within the solar system is more closely related to Earth life than life elsewhere in the galaxy, then this would be quite a good indication that some sort of local panspermia has occured.

Bringing the topic back to the original subject of this thread, we could also possibly be in a position to identify other stars which were once members of the Sun's birth cluster; it would be very interesting to find that life (if any) on planets surrounding those stars is more closely related to Earth life than life on planets surrounding other stars.

-------------------
I am trying very hard not to make any assumptions here, as I have all along; but it seems quite possible that some of the questions concerning panspermia and abiogenesis cannot in principle be resolved without examining a very large sample of stars and planets in our galaxy, and maybe not even then.

If options 2.1 and 3.1 both apply, then this could be the result of panspermia, or the result of a very tightly constrained form of abiogenesis. But (as I pointed out in an earlier post) even the genetic code mutates over time, so options 2.2 and 3.2 would be more realistic in practice, due to the fact that populations on different worlds are widely separated.


-------------------
We also can't rule out the transport of lifeforms by agents unknown, such as an advanced civilisation; this is sometimes called 'directed panspermia', but I prefer to use the term 'translocation', since it might also happen by accident. Translocation could even occur through the very same probes that a civilisation would use to look for life elsewhere in the galaxy. By sending dirty probes to the stars, we could bring life to the universe where it did not exist before.

If panspermia as a concept cannot ever be proved as a principle even if we examine large numbers of extrasolar systems, what use is it as a hypothesis? Well, I think it is in fact very useful, and will increase in usefulness over time. But because even if it ever happens it is a very rare event (probably occuring only rarely in the history of any planetary system if at all) we might never observe it occuring.

eburacum45
2012-Oct-14, 08:17 AM
Although we may never be able to observe panspermia in action, and therefore never be able to prove or disprove it, the same could apply to abiogenesis. Even if we manage to synthesise life which is biochemically identical to Earth life using a plausible pathway for abiogenesis, that would not prove that we had found the exact same pathway as occured on the ancient Earth. Even if we observe the same process happening on a distant terrestrial planet elsewhere, that would not prove it either. Basically both abiogenesis and panspermia will continue to remain hypotheses, even if we have got evidence for either or both.

Translocation, on the other hand, might be more easy to prove. In fact some people think it has already happened; see Reports of Streptococcus mitis on the moon
http://en.wikipedia.org/wiki/Reports_of_Streptococcus_mitis_on_the_moon
(although this seems to have been a mistake after all)

Colin Robinson
2012-Oct-14, 09:28 AM
I absolutely agree that we should avoid making any assumptions, but that doesn't mean we cannot consider the options methodically. I see the question as a set of options, which will (hopefully) be narrowed down if and when we find more data.

I'm impressed by your detailed and well-thought-out list of options....


1.2a/ there is some, but it is undetectable to our science because of unknown factors (it might be hiding, or otherwise impossible to detect).

That one reminds me of the question in Van Rijn's signature, about the invisible elf!


Now it is entirely possible that the life found within the solar system will be radically different to life found outside the solar system; in fact that seems to be very likely to me. If we find that life within the solar system is more closely related to Earth life than life elsewhere in the galaxy, then this would be quite a good indication that some sort of local panspermia has occured.

Yes!

Even within the solar system it is conceivable that we may find both life that is chemically and genetically very like Earth life, and also life that is very different. E.g. very Earth-like microbial life on Mars, very different life on Titan, very Titan-like life on Enceladus...

Which would be consistent with 2 abiogenesis events within this solar system, plus two instances of lithopanspermia.

Selfsim
2012-Oct-14, 09:58 AM
Even if we don't find life elsewhere in the solar system that doesn't mean that life is absent from the rest of the universe. One day, perhaps ....The test is all important.
If it can't be applied for whatever reason, (and it presently needs to be applied locally at the targetted specimen), then the hypothesis cannot be practically tested, and it therefore falls outside of the scientifc empirical process for the duration where it is not able to be applied. This is the case over a distance of not much greater than the radius of our Solar System and therefore, the idea of thinking about life beyond that distance seems futile .. (other than perhaps for dreaming, entertainment, theoretical investigations and political purposes).

Conclusions formed as a result of remote sensing of 'bio-signs', are entirely subject to the interpretive model assumptions, and we still only have one model for which those assumptions can be backed up with some empirical evidence. We still cannot rule out that such remotely sensed 'bio-signs' could be produced by as yet unknown processes not observed on Earth, which could be quite separate from what we'd relate to as 'life'. (Ie: false positives).

Until we have discovered and confirmed another instance of life within our reach, the interpretive model will be purely hypothetical and represents no greater value to empirical science, than a roll of a very big multi-faceted dice (die?), with a very large number of dots spread over each of the faces/facets.

Selfsim
2012-Oct-14, 10:03 AM
Even within the solar system it is conceivable that we may find both life that is chemically and genetically very like Earth life, and also life that is very different. E.g. very Earth-like microbial life on Mars, very different life on Titan, very Titan-like life on Enceladus...

Which would be consistent with 2 abiogenesis events within this solar system, plus two instances of lithopanspermia.All of which says nothing more than what Van Rijn's invisible elf says! (Given that I assert it is also capable of speech).

Colin Robinson
2012-Oct-14, 10:12 AM
All of which says nothing more than what Van Rijn's invisible elf says! (Given that I assert it is also capable of speech).

As someone else wrote a while back in another thread, microbial life on Mars (or Enceladus or Titan), is more comparable to a visible elf. If it's there, we'll be able to see it when we explore those places thoroughly.

Colin Robinson
2012-Oct-14, 08:20 PM
Credit where credit is due... The posting I had in mind is by Paul Wally, message # 685 in the thread "Evidence for ET..."


Of course it's not dependable, because we cannot depend on what has not been observed, but it is definitely verifiable. An invisible (Martian) elf is an example of something that is not verifiable. Visible elves on the other hand are verifiable. They're just not verified. There's a difference between "verifiable" and "verified".

Selfsim
2012-Oct-14, 10:45 PM
So can anyone disclose how a test which by necessity, has to be applied locally at the discovery site, can be executed (and then report the results), when the intervening distance is of the order of at least couple of light years?

Using the analogy, how do I see an elf which is hypothesised to exist light years away, (and tell everyone about it), when I've never seen one elsewhere, before*, and I can't bridge the distance needed, in order to be able to resolve its 'image', (so that I can 'see' it - at least to the degree of being able to reasonably exclude false positives)?

As I said, the hypothesis is legitimate in theory but for the time where the test cannot be applied (for practical reasons), the result remains the same in the real world, as if it wasn't. From an empirical science standpoint, for this reason, it cannot be presently verified, or said to be practically verifiable. From a theoretical standpoint, it is verifiable if the test exists, (and it doesn't violate the physical laws). It may be practically verified/falsified, depending on the 'non-rarity' factor assumed, but this assumption would be purely speculative. Practicality also limits our existence .. which could easily be argued why human return trips to the moon haven't occurred (post Apollo).

* Before anyone says we know life exists on Earth (ie: 'the elf'), we have never seen this type of life elsewhere. The idea that our idea of generalised life exists elsewhere, is the hypothesis we're testing … not that Earth-life, itself, can be tested. We can generalise part of the way to distinguish what we think might be a universal 'life' model, in theory ... but the tests for the possible ubiquity of this generalised 'universal' life model, still come back to being limited by practicality constraints, and by lack of precedent. (Ie: the interpretive models, lack the prior data needed in order for it to have legitimacy). This gap is plugged by a speculative premise .. ie: that Earth-like life exists elsewhere. There is circularity, (and fallacy), if this practicality aspect is not acknowledged. Evading the matter by retreating to some hypothetical future capability, cannot legitimately resolve this matter in the present, either.

PS: I can see this one being countered with word-play … (as usual)

eburacum45
2012-Oct-15, 07:05 AM
Evading the matter by retreating to some hypothetical future capability, cannot legitimately resolve this matter in the present, either.

I think that it is inevitable that we will have much more advanced automation and biotechnology by the time we are capable of sending probes to the stars. Tests to determine whether life exists on a planet will be considerably more advanced than those carried by Curiosity or any device we can build today.

Nevertheless it is entirely possible that even the most advanced autonomous biotechnology lab built by our descendants two or three hundred years from now will fail to detect some, or many, kinds of life or life-like processes. It might take decades or centuries of research to find the most deeply hidden types of life, just as we haven't found every type of life on Earth yet (and we probably never will).

Selfsim
2012-Oct-15, 08:54 AM
I think that it is inevitable that we will have much more advanced automation and biotechnology by the time we are capable of sending probes to the stars. Tests to determine whether life exists on a planet will be considerably more advanced than those carried by Curiosity or any device we can build today.You do get that this then, (ie: the logical premise), becomes entirely a matter of faith, right?


Nevertheless it is entirely possible that even the most advanced autonomous biotechnology lab built by our descendants two or three hundred years from now will fail to detect some, or many, kinds of life or life-like processes. It might take decades or centuries of research to find the most deeply hidden types of life, just as we haven't found every type of life on Earth yet (and we probably never will).So if the future you portray in your first paragraph is so certain, (ie: 'inevitable'), then why is it that the same future: 'probably never will find every type of life on Earth'?

You do get that the difference between the two scenarios of the future portrayed, is entirely a matter of faith and opinion, and has nothing to do with reality, right?

eburacum45
2012-Oct-15, 11:01 AM
You do get that this then, (ie: the logical premise), becomes entirely a matter of faith, right?

So if the future you portray in your first paragraph is so certain, (ie: 'inevitable'), then why is it that the same future: 'probably never will find every type of life on Earth'?

You do get that the difference between the two scenarios of the future portrayed, is entirely a matter of faith and opinion, and has nothing to do with reality, right?

If we have technology sophisticated enough to go to the stars, we will almost certainly also have more sophisticated biotechnology than today; some people seem to think that biotech and automation will stand still for the next two hundred years and fail to progress. That is unlikely to be the case.

However sophisticated automation and biotechnology will become, there is no guarantee that together they will allow us to find every possible kind of lifeform, either on Earth or on a planet around a distant star. That shouldn't stop us from looking, though.

Colin Robinson
2012-Oct-15, 11:59 AM
So can anyone disclose how a test which by necessity, has to be applied locally at the discovery site, can be executed (and then report the results), when the intervening distance is of the order of at least couple of light years?

The test for what would involve a distance of at least a couple of light years?


The idea that our idea of generalised life exists elsewhere, is the hypothesis we're testing …

If that's the hypothesis you want to test, why do you think it would be necessary to go "at least" a couple of light-years to test it?

Is Mars a couple of light-years away? Is Europa? Is Titan? Is Enceladus?

If life can be found in any of these places, won't that verify the hypothesis that life exists elsewhere than Earth?


PS: I can see this one being countered with word-play … (as usual)

What do you think you accomplish by such a generalized negative statement?

A.DIM
2012-Oct-15, 02:18 PM
All: Thank you for your involvement and interesting contributions. Apologies I've not been available to help keep you on topic. ;)
I have however, managed to finish the paper (http://arxiv.org/pdf/1205.1059.pdf) on which the OP is based. It's a good paper and I agree with its premise: If life arose early enough, either on Earth (for which there is evidence) or elsewhere in the sun's maternal cluster, and before cluster dispersal, this weak transfer mechanism suggests life could spread easily. As to whether it originated on Earth and was spread elsewhere or was transported to Earth from elsewhere ... how could we know? Personally I don't think we can.

John Jaksich: Thanks for the reference on Fuller. I'll read more as time permits. Such a discussion is not for this thread however.

Paul Wally
2012-Oct-21, 01:54 AM
* Before anyone says we know life exists on Earth (ie: 'the elf'), we have never seen this type of life elsewhere. The idea that our idea of generalised life exists elsewhere, is the hypothesis we're testing … not that Earth-life, itself, can be tested. We can generalise part of the way to distinguish what we think might be a universal 'life' model, in theory ... but the tests for the possible ubiquity of this generalised 'universal' life model, still come back to being limited by practicality constraints, and by lack of precedent. (Ie: the interpretive models, lack the prior data needed in order for it to have legitimacy). This gap is plugged by a speculative premise .. ie: that Earth-like life exists elsewhere. There is circularity, (and fallacy), if this practicality aspect is not acknowledged. Evading the matter by retreating to some hypothetical future capability, cannot legitimately resolve this matter in the present, either.


Define "Earth-like life". What are the characteristically Earth-like features. If you cannot give criteria for what distinguishes "Earth-like life" from non-earth-like life then "Earth-like life" is not testable and therefore not scientifically meaningful.