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wd40
2013-Nov-04, 09:07 PM
If this study is correct then have the odds for life in the galaxy just risen dramatically?

Study: 8.8 billion Earth-sized just-right planets
http://www.ynetnews.com/articles/0,7340,L-4449559,00.html

schlaugh
2013-Nov-04, 09:24 PM
That story is a bit abbreviated. The NY Times has a significantly longer version. (http://www.nytimes.com/2013/11/05/science/cosmic-census-finds-billions-of-planets-that-could-be-like-earth.html?hp&_r=0)

And here's an abstract of the paper. (http://www.pnas.org/content/early/2013/10/31/1319909110)

Basically the researchers conducted a sophisticated process of extrapolating how many Earth-like worlds could exist in habitable zones in the Milky Way. Some of the key criteria they used in their selection method were one to two Earths in mass, and a fairly wide habitable zone receiving 0.25 to 4.0 times the amount of solar radiation received by the Earth.

Selfsim
2013-Nov-04, 10:31 PM
If this study is correct then have the odds for life in the galaxy just risen dramatically?

Study: 8.8 billion Earth-sized just-right planets
http://www.ynetnews.com/articles/0,7340,L-4449559,00.htmlThe inferences drawn from the model are purely hypothetical, therefore the inferences cannot be said to be 'correct' or 'incorrect'.

The distribution of life throughout the galaxy remains: 'Unknown', regardless of this study or of the model.

There is no evidence that the distribution of life throughout the galaxy, (or even in the Kepler sample), is a matter of random chance, nor is it purely a matter of 'odds'.

Githyanki
2013-Nov-05, 02:58 AM
But surely you can calculated the odds of a planet forming within the average HZ and it's probable size; I wouldn't all a world like that, "Earth-like", just a possible Earth-like world (Venus/Mars could also be a result)

Selfsim
2013-Nov-05, 05:45 AM
But surely you can calculated the odds of a planet forming within the average HZ and it's probable size; I wouldn't all a world like that, "Earth-like", just a possible Earth-like world (Venus/Mars could also be a result)Yep ...

Does the 'Earth-like worldness' of Venus or Mars imply that it is 'likely' that there is life on Venus or Mars?

NEOWatcher
2013-Nov-05, 12:31 PM
If this study is correct then have the odds for life in the galaxy just risen dramatically?
No, the odds have not changed. Only our estimate has changed.


But surely you can calculated the odds of a planet forming within the average HZ and it's probable size; I wouldn't all a world like that, "Earth-like", just a possible Earth-like world (Venus/Mars could also be a result)
That was my thought as well. I feel the "Earth's", "Earth-like", and "Super Earth" are phrases that are much overrused.
When I think Earth-like, then I think of the overall surface conditions, not just size and location.

I'm sure everyone draws their own line where that is, but my line won't be drawn for a very long time since it requires much more detail.

iquestor
2013-Nov-05, 01:59 PM
No, the odds have not changed. Only our estimate has changed.


That was my thought as well. I feel the "Earth's", "Earth-like", and "Super Earth" are phrases that are much overrused.
When I think Earth-like, then I think of the overall surface conditions, not just size and location.

I'm sure everyone draws their own line where that is, but my line won't be drawn for a very long time since it requires much more detail.

Yes, our estimate has changed.

I think people confuse 'earth-like' and 'super earth' like they do 'UFO' - They read or hear UFO and think 'Alien', where all it means is 'we dont know what it is, its unidentified'.
So when they hear 'earth-like' the connotation is that its in the HZ with an atmosphere and liquid water, and probably life. which of course, isn't true.

I think they need to come up with a better term, but if it's 'Earth-' anything is in the name, it amounts to the same problem.

Noclevername
2013-Nov-05, 02:06 PM
"Terrestroid", as a cognate to "humanoid"?

NEOWatcher
2013-Nov-05, 02:09 PM
I think they need to come up with a better term, but if it's 'Earth-' anything is in the name, it amounts to the same problem.
At least Fraser used the term "Earth-Sized" which narrows down what they are looking at. Even at the liberal size range, it's still narrow based on the sizes of other types of planets.

Ken G
2013-Nov-05, 02:43 PM
The bottom line is, they found 10 Earth-sized planets at a life-interesting distance from a life-interesting star, out of 42,000 such stars. You can pretty much draw your own conclusions from that, this is the only fact that the article is based upon. However, it is an important fact-- we didn't know if that number would be zero or 1,000, so it's interesting that it's 10. It's not a big surprise, frankly, but it rules out the possibility that planets that might conceivably host life are exceedingly rare. What we still don't know is how many that could "conceivably" host life actually do-- and we are never going to know that until we actually find life somewhere else.

ETA: To follow that up a bit, the two major uncertainties in the issue of life elsewhere are, how likely is it for life to get started in an environment that is conducive to it, and how long does it last in such an environment (including, how long does the environment remain conducive, or does it suffer rapid or extreme variations). We can't use Earth to answer any of those questions, because of the anthropic principle (we have to be here). So right now it looks like Mars and Venus are the keys. Did life get started on either of those? If so, how long did it last? We really have no idea what the answers to those questions are, and until we do, it's just a complete guessing game. Throw in our interest in the likelihood of life developing intelligence, and the impact of having intelligence on the longevity of a species, and the issue becomes completely uncertain. Finding Earth-sized planets is an interesting step, but it's like the first step in a weeklong hike. But observing oxygen in the atmospheres of extrasolar planets might be a huge breakthrough along those lines.

Trebuchet
2013-Nov-05, 02:47 PM
Some guy named Plait has a blog post (http://www.slate.com/blogs/bad_astronomy/2013/11/04/earth_like_exoplanets_planets_like_ours_may_be_ver y_common.html) on the subject.

jfribrg
2013-Nov-05, 04:04 PM
I haven't seen the original paper ( and probably wouldn't understand it if I did), but there are a couple of assumptions that I haven't seen addressed. The discussions I've seen assume that stars are equally likely to have planets regardless of where they are located in the galaxy. It seems to me that stars in dense clusters and especially stars near the central bulge would have far fewer planets than ones farther away because with stars near each other, stable orbits would be less likely. I'm also curious about the assumption that 10% of stars in the galaxy are Sun-like. With so much mass concentrated near the center, one would expect an overabundance of much larger stars near the center.

iquestor
2013-Nov-05, 05:59 PM
Some guy named Plait has a blog post (http://www.slate.com/blogs/bad_astronomy/2013/11/04/earth_like_exoplanets_planets_like_ours_may_be_ver y_common.html) on the subject.



thanks for that link. it was excellent!

NEOWatcher
2013-Nov-05, 06:01 PM
What we still don't know is how many that could "conceivably" host life actually do-- and we are never going to know that until we actually find life somewhere else.
At this point, I'm not even sure we have a good grasp of how many "could conceivably" host life. We are working on candidates that could conceivably host life.

I was reading an explaination of their process (and only half paying attention to the numbers), and there are plenty of averages and assumptions in there.

Considering we are only working on parameter 3 of the 6 parameter Drake equation, we have a long way to go before we make any speculations on life.

Of course, the media is not going to portray it that way. One article talked about one "Earth-like" planet for every person on Earth. I wouldn't want to be the one that ends up on a Venus-like Earth-like planet.

kevin1981
2013-Nov-05, 06:59 PM
I think that most of us wish there was other life and that we had some sort of contact. I have heard many people say to me, because of the vast numbers, "there must be other life out there" ! However, what i have learnt from coming on here is, that is not true. "There must be" is not a scientific answer, it is wishful thinking. Evidence is key, at the moment the only answer is, we do not know. We do not know how life started, we do not know if life gets going quickly, we do not know if life gets going quickly under the right environmental conditions and so on... The only thing we know at this point is, the chance of life arising in the observable universe is not zero.

Life is hard sometimes, but i am very thankful for this opportunity to be taking part in it.

NoisyAstronomer
2013-Nov-05, 07:20 PM
A copy of the paper has been posted outside of the paywall, for those interested: http://cosmo.nyu.edu/hogg/research/2013/11/05/petigura_etal.pdf

Githyanki
2013-Nov-05, 11:43 PM
I read the short-article and I agree with most of it: a few years ago, I added up all the HZs in the local star group and did a few other things I've forgotten because it was a few years ago and I didn't write it down and I got 17% chance of a planet being in an HZ; now, since a class F or G star will have a larger HZ, there's more of a chance of a world in those systems having liquid water. So I agree with the 22%.

But I must stress that because a world is in the HZ, doesn't mean it's Earth-like. If you have a star with a low-metallicity, you may have only a Mars-like world in the HZ, hardly Earth-like.

Until every single star in the milky-way is found to have planets, the data will always be slanted towards Hot-Jupiters just because they are the easiest to find.

Van Rijn
2013-Nov-06, 09:53 AM
A copy of the paper has been posted outside of the paywall, for those interested: http://cosmo.nyu.edu/hogg/research/2013/11/05/petigura_etal.pdf

Thanks!

iquestor
2013-Nov-06, 01:07 PM
At this point, I'm not even sure we have a good grasp of how many "could conceivably" host life. We are working on candidates that could conceivably host life.

I was reading an explaination of their process (and only half paying attention to the numbers), and there are plenty of averages and assumptions in there.

Considering we are only working on parameter 3 of the 6 parameter Drake equation, we have a long way to go before we make any speculations on life.

Of course, the media is not going to portray it that way. One article talked about one "Earth-like" planet for every person on Earth. I wouldn't want to be the one that ends up on a Venus-like Earth-like planet.

<bold, mine>... I don't think we should or can ever speculate life; I think we should pursue direct evidence. The only direct evidence ( I don't say proof) we will have anytime soon (unless a landing on the White House Lawn is in our future) will be via spectroscopy.
detection of radium, thorium, along with methane + oxygen in some form, along with water vapor would be very, very compelling evidence on a known rocky planet within its HZ ( or, perhaps, an exo-moon).

NEOWatcher
2013-Nov-06, 01:28 PM
<bold, mine>... I don't think we should or can ever speculate life; I think we should pursue direct evidence. The only direct evidence ( I don't say proof) we will have anytime soon (unless a landing on the White House Lawn is in our future) will be via spectroscopy.

Are you agreeing or disagreeing? I did say "a long way to go". Who knows what the far future may bring in detection technology?

Noclevername
2013-Nov-06, 01:43 PM
<bold, mine>... I don't think we should or can ever speculate life; I think we should pursue direct evidence.

I don't think we should ever assume life. Speculating about possible life as a thought-experiment, based on existing knowledge, is fine as long as you make sure it's clear this is just a mental simulation and do not draw conclusions from it or encourage other to. The article fails by miles to make that distinction.

NEOWatcher
2013-Nov-06, 02:03 PM
We're not going to head down that path (http://cosmoquest.org/forum/showthread.php?144018-My-Frustration-with-the-Life-In-Space-forum) again, are we?

Noclevername
2013-Nov-06, 02:08 PM
We're not going to head down that path (http://cosmoquest.org/forum/showthread.php?144018-My-Frustration-with-the-Life-In-Space-forum) again, are we?

I just thought the term "speculate life" was a little too vague. Having clarified the point, I'm dropping it now.

Swift
2013-Nov-06, 02:26 PM
We're not going to head down that path (http://cosmoquest.org/forum/showthread.php?144018-My-Frustration-with-the-Life-In-Space-forum) again, are we?
It seems unlikely that this thread can go any other way. As this is not a straight-forward question, and is almost certain to turn into an extended discussion, I'm moving the thread from Q&A to LiS.

Spacedude
2013-Nov-06, 02:59 PM
If we're just talking about simple single celled life forms we may not need to restrict the parameters to earth sized planets within a habitable zone around a star. The moons of Jupiter and Saturn could well turn everything on it's head.

wd40
2013-Nov-06, 05:22 PM
If solid new evidence was found or new models developed that whilst not disproving evolution on this Earth, but showing that the chances of it occurring on any other planet were so vanishingly close to zero that the search for extra terrestrial life that costs billions of tax $$$ was virtually in vain or an exercise in futility, is it conceivable that that search be scaled down in any way? Or will the inquisitiveness of the human spirit and the vested interests of agencies and departments never allow it?



We do not know how life started, we do not know if life gets going quickly, we do not know if life gets going quickly under the right environmental conditions and so on... The only thing we know at this point is, the chance of life arising in the observable universe is not zero.

Noclevername
2013-Nov-06, 05:40 PM
If solid new evidence was found or new models developed that whilst not disproving evolution on this Earth, but showing that the chances of it occurring on any other planet were so vanishingly close to zero that the search for extra terrestrial life that costs billions of tax $$$ was virtually in vain or an exercise in futility, is it conceivable that that search be scaled down in any way? Or will the inquisitiveness of the human spirit and the vested interests of agencies and departments never allow it?

That's an unanswerable question. We can't find solid evidence to prove a negative, and models vary greatly by starting parameters. There already exist models that show Earth must be unique. Those models are not generally given much credence by the scientific community at large because many contain assumptions that are skewed towards a particular result or do not take all observations into account. Models are like the Drake Equation, plug in your own guesswork values and you can get answers from one to unlimited.

jfribrg
2013-Nov-06, 06:52 PM
A copy of the paper has been posted outside of the paywall, for those interested: http://cosmo.nyu.edu/hogg/research/2013/11/05/petigura_etal.pdf

Thanks for the link.

Why am I not surprised that the authors of the paper were far more careful in their conclusions than everyone else. They reached no conclusion that the galaxy was teeming with Earth-like planets. They only concluded that 22% of the Sun-like stars in our region of the galaxy had Earth-like planets. They did not analyze the distribution of sun-like stars in the rest of the galaxy, and so you cannot extrapolate the results of this sample. The main conclusion is that an Earth-like exoplanet is probably somewhere within approximately 12 LY of us.

iquestor
2013-Nov-06, 07:05 PM
Are you agreeing or disagreeing? I did say "a long way to go". Who knows what the far future may bring in detection technology?

I was agreeing with you. I felt you were saying we were no where near being able to answer or even discuss the life questions. Until we have some real evidence, I'd agree.. sorry I wasn't more clear.

iquestor
2013-Nov-06, 07:10 PM
I don't think we should ever assume life. Speculating about possible life as a thought-experiment, based on existing knowledge, is fine as long as you make sure it's clear this is just a mental simulation and do not draw conclusions from it or encourage other to. The article fails by miles to make that distinction.

I agree. we can't assume life until we have a basis on which to assume it. I can safely assume there is life in some extreme places on Earth because we have shown it can an does exist practically everywhere we look. we arent there yet for exoplanets. Once we do find several examples of life on different planets (IF it exists) , perhaps we can then draw some assumptions.

However, such speculations about life, properly framed, are fine in context of LiS. We have discussed it before. My earlier comment about specualtion on life wasnt about this forum, it was a statement about scientists and authors speculating on life as if it were a foregone conclusion... My comment had nothing to do regarding LiS disucssions.

Noclevername
2013-Nov-06, 07:16 PM
I agree. we can't assume life until we have a basis on which to assume it. I can safely assume there is life in some extreme places on Earth because we have shown it can an does exist practically everywhere we look. we arent there yet for exoplanets. Once we do find several examples of life on different planets (IF it exists) , perhaps we can then draw some assumptions.

However, such speculations about life, properly framed, are fine in context of LiS. We have discussed it before. My earlier comment about specualtion on life wasnt about this forum, it was a statement about scientists and authors speculating on life as if it were a foregone conclusion... My comment had nothing to do regarding LiS disucssions.

OK, thanks, I appreciate that you made that clear. I for one am a little over-sensitive on the subject of another rehash!

ravens_cry
2013-Nov-07, 12:00 AM
You know, on the off chance the warp field interferometer experiments (http://en.wikipedia.org/wiki/White%E2%80%93Juday_warp-field_interferometer)pan out, we may just visit some of those 8.8 billion Earth's. Not today, not in my lifetime barring revolutionary advances in longevity, but someday potentially.

Noclevername
2013-Nov-07, 01:05 AM
You know, on the off chance the warp field interferometer experiments (http://en.wikipedia.org/wiki/White%E2%80%93Juday_warp-field_interferometer)pan out, we may just visit some of those 8.8 billion Earth's. Not today, not in my lifetime barring revolutionary advances in longevity, but someday potentially.

We may never get FTL (Faster Than Light) but IIRC, some studies suggest that a warp drive could get us NTL (Near To Light).

ravens_cry
2013-Nov-07, 01:27 AM
We may never get FTL (Faster Than Light) but IIRC, some studies suggest that a warp drive could get us NTL (Near To Light).
Good enough for me. If people can survive this (http://en.wikipedia.org/wiki/Nansen%27s_Fram_expedition), I think they can stand the isolation of a multi-year voyage to the stars with modern distractions.

Noclevername
2013-Nov-07, 11:58 AM
Good enough for me. If people can survive this (http://en.wikipedia.org/wiki/Nansen%27s_Fram_expedition), I think they can stand the isolation of a multi-year voyage to the stars with modern distractions.

Time dilation would make the trip seem shorter; at least that's true for conventional drives, I'm not sure the same rules would apply to a ship in a bubble of warped spacetime.

iquestor
2013-Nov-07, 02:08 PM
OK, thanks, I appreciate that you made that clear. I for one am a little over-sensitive on the subject of another rehash!

Yep. I should be more careful using the term speculating :D Its a dangerous word here, one fraught with dragons and other hazards.... :D

ravens_cry
2013-Nov-07, 09:02 PM
Time dilation would make the trip seem shorter; at least that's true for conventional drives, I'm not sure the same rules would apply to a ship in a bubble of warped spacetime.
From what I've heard, (http://en.wikipedia.org/wiki/Alcubierre_drive#Alcubierre_metric)they don't unfortunately. Space is being squeezed and stretched, but no one is actually moving per sae. That's probably the lies to children explanation at least.

Noclevername
2013-Nov-08, 06:39 AM
That's probably the lies to children explanation at least.

"...And if you're really good, the Alcubierre Fairy will leave a warp drive under your pillow!"

ravens_cry
2013-Nov-08, 07:07 AM
"...And if you're really good, the Alcubierre Fairy will leave a warp drive under your pillow!"
Don't I wish. What I mean is, an explanation that aids understanding within certain limits while not in itself being true. Like the classic 'solar system' model of the atom.

Noclevername
2013-Nov-08, 08:01 AM
Don't I wish. What I mean is, an explanation that aids understanding within certain limits while not in itself being true. Like the classic 'solar system' model of the atom.

I thought that was what you meant, but I couldn't resist going for the joke. I also have a nice selection of Santa Claus gags available.

ravens_cry
2013-Nov-08, 08:33 AM
I thought that was what you meant, but I couldn't resist going for the joke. I also have a nice selection of Santa Claus gags available.
I am sure astrophysicists would love to get a lump of coal in their stocking. It is dark matter after all.

Noclevername
2013-Nov-08, 08:40 AM
I am sure astrophysicists would love to get a lump of coal in their stocking. It is dark matter after all.

:rimshot:

ravens_cry
2013-Nov-08, 09:38 AM
:rimshot:

Thank you, thank you, we'll be here all night. Try the unicorn milk; it's legend dairy.:D

kzb
2013-Nov-21, 01:18 PM
It's a pity that discussioin of the actual paper has been diverted so quickly. It's a very discussable paper I think.

First point, what do people think about the classification of planets with twice the diameter of Earth as potential "Earths" ?

Second, on other websites, I have seen the extent of the habitable zone in this paper described as outrageous. The luminous flux on the planet could be up to 4X that of Earth. The authors do state however that their HZ is a long way from being the most extensive HZ ever described.

Third, and on the other hand, sub-Earths are seemingly not estimated and included in the figures. Likewise, only the highest signal to noise planet in a system is included, which would exclude enumeration of Earths co-planar with the very common close-orbiting super-Earths.

Another comment not orginal to me I am sure, but every single planet in our own system is far into the dark shaded region of almost indetectabilty in their Figure 1. We are still having to extrapolate and make inferences about the occurrence of true Earth analogues even after Kepler. It broke down too early to complete its mission.

That said, this paper is surely just a start. Please don't interpret this as a negative criticism of the paper because it's not. I am sure there is a lot more to be made out of the Kepler data yet.

kzb
2013-Nov-27, 12:54 PM
Just to say, the paper has now appeared on arxiv:

Prevalence of Earth-size planets orbiting Sun-like stars
Authors: Erik A. Petigura, Andrew W. Howard, Geoffrey W. Marcy


http://arxiv.org/abs/1311.6806

neilzero
2013-Nov-27, 04:41 PM
If the average density is half that of Earth, 6000 kilometers,radius only produces about 2g of surface gravity especially if the low density is mostly in the crust.

kzb
2013-Nov-27, 06:38 PM
But the Earth is 6000km in radius. A planet with twice the radius of Earth is huge, nearly 16,000 miles diameter. It was not so much the surface gravity I was thinking about anyway.

I was wondering more generally, how can such a planet be anything like Earth? Is this possible?

KABOOM
2013-Nov-28, 03:13 PM
So if Earth as a baseline is 1.0, what is the generally accepted range of planet size in which Earth-like attributes (rockiness, plate tectonics, magnetic shields, etc) "could" exist? I've seen things like 0.5 to 2.0 but just anecdotally. How well do we really know the answer to this question given our scarcity of observations?

Number 16 Bus Shelter
2013-Nov-29, 05:27 PM
I find it extremely likely that there is life out there in the universe, even if it is not in out galaxy.

The thing is that we are looking for Earth like planets, when actually life can exist in different planets. There may be thousands of ways life can exist in hostile conditions that we are unaware of. If right now on Earth there are several species of bacteria which can live in extreme conditions, why can't this kind of being be out there as well?

Noclevername
2013-Nov-30, 02:24 AM
I find it extremely likely that there is life out there in the universe, even if it is not in out galaxy.

My opinion is that life is possible elsewhere, but it's just an educated guess. If, where and how common are all at present unanswered questions; the only way we can say for sure, is by actually observing life elsewhere.


The thing is that we are looking for Earth like planets, when actually life can exist in different planets. There may be thousands of ways life can exist in hostile conditions that we are unaware of. If right now on Earth there are several species of bacteria which can live in extreme conditions, why can't this kind of being be out there as well?

(bold mine)

Life might be able to exist on different kinds of planets. Yes, extremophiles exist on Earth, but we don't know quite what precise conditions led to life forming in the first place and how they adapted to extreme environments from a common ancestry, so to say that life can exist on non-Earthlike planets is premature at this point.

ravens_cry
2013-Dec-01, 01:55 AM
Exactly. We can hope, we can dream, we can conjecture and we can guess, but we can't know until we know, you know?

kzb
2013-Dec-03, 05:56 PM
I find it extremely likely that there is life out there in the universe, even if it is not in out galaxy.

The thing is that we are looking for Earth like planets, when actually life can exist in different planets. There may be thousands of ways life can exist in hostile conditions that we are unaware of. If right now on Earth there are several species of bacteria which can live in extreme conditions, why can't this kind of being be out there as well?

Yep, but if you widen out the possibilities like this, there are potentially many inhabited worlds in our own solar system. Earth, Mars, Europa, Titan, Enceladus, maybe even Ceres and Pluto. Anywhere that liquid water is possible.

If an inhabited world is classed as these kinds of world, populated by extremophile microorganisms, there are probably trillions of them in the galaxy.

Kepler was about finding Earth-like worlds. Probably with the idea that these are capable of having the surface-living complex life that people are most interested in.

TooMany
2013-Dec-04, 09:12 PM
You can widen possibilities even more if liquid water can exist inside comets, perhaps warmed by radioactive elements. See http://www.space.com/11307-comet-samples-liquid-water-stardust.html

Suppose life gets it's start in the trillions of comet-like bodies that formed when the solar system formed. Such life could seed planets capable of supporting life without the necessity of the planet giving rise to life.

Typically any hints of panspermia, even on just the solar system level, give rise to extreme skepticism from the mainstream.

Noclevername
2013-Dec-06, 02:44 PM
You can widen possibilities even more if liquid water can exist inside comets, perhaps warmed by radioactive elements. See http://www.space.com/11307-comet-samples-liquid-water-stardust.html


The water-formed minerals in the comets could have been picked up from a colliding planetesimal during the formative years of the Solar System.

TooMany
2013-Dec-07, 07:07 AM
The water-formed minerals in the comets could have been picked up from a colliding planetesimal during the formative years of the Solar System.

Not sure but is a planetesimal something different from a comet that has liquid water which a comet does not?

Noclevername
2013-Dec-07, 07:26 AM
Not sure but is a planetesimal something different from a comet that has liquid water which a comet does not?

It's the matrix of a forming planet. It's possible that some of them could have had periods of liquid water, especially during the period when they had lots of impacts and when radioactive decay had just begun.