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RafaelAustin
2003-Apr-04, 09:40 PM
Just thought it would be interesting to compose a list of possible astronomy related requirements for life on Earth or other worlds. For the sake of this argument I'll limit it to life that we would be familiar with and/or biosystems that would resemble our own. This could also be looked at as worlds that would be favorable for our colonization. I'll update this list as everyone contributes to it, looking forward to everyone's input. For controversial theories, I'll provide a link.

* 2nd generation star w/ heavy elements
* Large planetary family to absorb debris
* Iron core to generate magnetosphere
* Planet massive enough to retain atmosphere
* Collision w/ planetoid to create voids in tectonic plates and large moon LINK (http://www.spacedaily.com/news/life-01x1.html)
* Large moon to stabilize rotation
* Plate tectonic activity
* Water by cometary seeding
* Recent nearby nova to clear out interstellar dust LINK (http://cse.ssl.berkeley.edu/chips_epo/science.html)
* Time between large impacts for life
* Main sequence star LINK (http://homepage.sunrise.ch/homepage/schatzer/Alpha-Centauri.html)
* Spectral type: G, late F, early K
* Stable intensity of star
* Adequate age for life to evolve
* Orbit within 'habitable zone'
* Avoid close orbit and being tidally locked to star
* Not within a dense star cluster
* Sudden, occasional environmental/ecological changes to encourage evolution

* Catalog of Nearby Habitable Planets (http://www.astrobio.net/news/modules.php?op=modload&name=News&file=article&sid=436&mode=thread&order=0&thold=0)


Thanks all for your input! :)

skeptED56
2003-Apr-04, 09:48 PM
"* G type star "

Not neccesarrily, a late F or early K type star are also candidates for having life-bearing planets.

I found a link with a nice table that shows the possibilies for habital planets in the Alpha Centauri System. The five tests can apply for all stars.

http://homepage.sunrise.ch/homepage/schatzer/Alpha-Centauri.html

g99
2003-Apr-04, 09:53 PM
-planet massive enougth to hold a substancial atmosphere

skeptED56
2003-Apr-04, 10:00 PM
*Reasonable amount of time between large "impactors"

RafaelAustin
2003-Apr-04, 10:13 PM
*Reasonable amount of time between large "impactors"

That might actually go both ways. Catastophic events might be required to increase the likelyhood of evolution.

Thanks for the input everyone. I'm curious to see what other lesser known circumstances help make life possible. I tend to think we are in a very special condition here on Earth.

ToSeek
2003-Apr-04, 10:29 PM
The Rare Earth folks claim that you need to be in a certain part of the galaxy, neither too far in nor too far out. I don't recall the background for that claim, though.

nexus
2003-Apr-04, 11:09 PM
I believe the position in the galaxy relates to the amount of heavy elements and the proximity of other stars, Astronomy Magazine had an article about it around six months ago.

beskeptical
2003-Apr-04, 11:38 PM
Without specific argument for or against all these requirements, one has to keep an open mind. We are only familiar with the components that resulted in life on Earth. Recent discoveries of life in extreme environments has shown past assumptions about the limits of life were wrong.

I would say we know that certain conditions are capable of supporting life but at this point we can't say that these are all minimum requirements.

RafaelAustin
2003-Apr-05, 01:36 AM
I agree. I'm sure that eventually we will be amazed at the variety of Life and the conditions which it can form and thrive, but I'm just trying to catalog what we know or theorize about 'Earth-like' conditions for life as we know it. Maybe I should re-title this as a list of possible factors for the emergence of life on Earth. I just think that it's amazing that there are so many significant events that have contributed.

Glom
2003-Apr-05, 09:21 AM
Could say a B type star also have a habitable zone a bit further away than a G type star would?

Why would a large moon be necessary to stabilise rotation. By Newton I, once a body is rotating, it will continue to do so.

darkhunter
2003-Apr-05, 10:10 AM
Saw on BBC Horizon (http://www.bbc.co.uk/science/horizon/) about Carlsbad Caverns where they've found evidence that life originated underground (and acutally ate away the rock to make the caves...This protected it from the impacts of meteorites on a still forming infant earth...

Also brought up about the extreme-loving microbes that live in conditions that would normally destroy other life, so life could be more common than otherwise thought, especially at the unicellular level.

My question is: Clould these evole ofer time to mulicellular (even intellegent) life adapted to such extreme conditions? This could open up the "inhabitable zone" some and broaden the catagory of stars to search thru....

David Hall
2003-Apr-05, 10:13 AM
Why would a large moon be necessary to stabilise rotation. By Newton I, once a body is rotating, it will continue to do so.

It's not that the planet would stop rotating, it's that without the Moon, the rotational axis would be unstable. The planet would wobble up to 90& over time. Mars apparently shows this kind of wobble. Discovery channel here had a show last week on what would happen if there were no Moon, and this was one of the biggies.

Kaptain K
2003-Apr-05, 10:48 AM
Could say a B type star also have a habitable zone a bit further away than a G type star would?

Yes, but! There are two problems with type B stars:
1) High levels of UV radiation would be lethal to life as we know it.
2) B type stars don't live very long. With main sequence times of less than a billion years, there just isn't enough time for life to do more than just get started.

Glom
2003-Apr-05, 11:05 AM
It's not that the planet would stop rotating, it's that without the Moon, the rotational axis would be unstable. The planet would wobble up to 90& over time.

But what causes the wobble and how would this threaten the development of life.


Yes, but! There are two problems with type B stars:
1) High levels of UV radiation would be lethal to life as we know it.
2) B type stars don't live very long. With main sequence times of less than a billion years, there just isn't enough time for life to do more than just get started.

Fair enough. What about an M type star? If the planet orbited within a much closer distance than Earth about Sol, could life develop there?

skeptED56
2003-Apr-05, 03:22 PM
Glom Wrote

What about an M type star? If the planet orbited within a much closer distance than Earth about Sol, could life develop there?


The problem with M type stars is they don't produce enough energy. If a habital zone did exist it would be very small, and even then the energy ouput wouldn't be nearly as big, plants would have a very hard time.[/b]

Kaptain K
2003-Apr-05, 03:46 PM
Glom Wrote

What about an M type star? If the planet orbited within a much closer distance than Earth about Sol, could life develop there?


The problem with M type stars is they don't produce enough energy. If a habital zone did exist it would be very small, and even then the energy ouput wouldn't be nearly as big, plants would have a very hard time.[/b]
I must disagree here (at least slightly). While it is true that M type dwarfs produce little energy, that just means that the habitable zone is closer to the star. Get close enough to the star and you will find a distance at which the energy received by the planet is suficient to keep the surface of the planet warm enough for life as we know it.

skeptED56
2003-Apr-05, 04:10 PM
Glom Wrote

What about an M type star? If the planet orbited within a much closer distance than Earth about Sol, could life develop there?


The problem with M type stars is they don't produce enough energy. If a habital zone did exist it would be very small, and even then the energy ouput wouldn't be nearly as big, plants would have a very hard time.[/b]
I must disagree here (at least slightly). While it is true that M type dwarfs produce little energy, that just means that the habitable zone is closer to the star. Get close enough to the star and you will find a distance at which the energy received by the planet is suficient to keep the surface of the planet warm enough for life as we know it.

Ok it may be possible for life to evolve around an M type star. But wouldn't it also subject a planet that close to an M type star to more harmful (or would be harmful to life as we know it) radiation? And warmth isn't everything, plants would have a harder time collecting energy, limiting the total amount of energy in a given ecosystem, right?

Let's take for example Proxima Centauri, its an M5 type star and only has .00006 Sol's brightness, how close to the star can you get?

RafaelAustin
2003-Apr-05, 04:16 PM
It seems reasonable that there would be an orbit close enough to a Type M star to have liquid bodies of water. And for Type K stars, what if the planet had a larger magentic field than we do, or a thick cloud cover?

After thinking about this and reading the list it seems that promoting long term stability is the biggest factor. Stable orbits, rotation, climate, stellar environment, etc. Seems that the recipe for Life is 'bake at 300K for 3 billion years'! :D And don't open the oven or the cake will fall!

snowcelt
2003-Apr-05, 04:23 PM
And too add to skeptE56's remark "how close to the star can you get?" What are the chances of having the perfect planet in the very small life zone afforded by a star with such minimal energy.

Kaptain K
2003-Apr-05, 05:56 PM
Upon further reflection, I think the biggest problem with M type dwarfs would be that the habitable zone would be so close to the star that the planet would be tidally locked with the star. giving permanent daylight on one side and permanent night on the other. :o

RafaelAustin
2003-Apr-05, 06:57 PM
Great point! So it seems a minimum distance would also be required for an Earth-like world.

skeptED56
2003-Apr-05, 06:57 PM
I agree that a planet that close could become tidally locked with star, causing a problem for life as we know it. But I disagree that it would be the "biggest problem." I think the reduced energy output and the fact that closer proximity to the star may result in more harmful radiation would pose equal if not bigger problems. As long as the atmosphere is thick enough, becoming tidally locked would not become a huge problem for life (at least on the day side). But it does add to a list of problems with M type stars. :D

RafaelAustin
2003-Apr-05, 07:07 PM
I remember a discussion relating to this on BABB a few months ago. The topic was Terraforming Venus and the problems associated with it having such a long day. I don't remember if a theorhetical plan to overcome this was ever brought up.

Ah, found the link (http://www.badastronomy.com/phpBB/viewtopic.php?mode=viewtopic&topic=3260&forum=2&start=0).

Kaptain K
2003-Apr-05, 07:11 PM
Its not the energy output of the star that matters. It is the energy influx to the planet. If the output of the star is less, the planet just needs to be closer to the star for the influx to be the same.

The energy spectrum might be a problem. Since the output of a M dwarf is mostly IR and red, with little blue and almost no UV, photosynthesis would probably be based on something with a different response curve than chlorophyll.

skeptED56
2003-Apr-05, 07:32 PM
Its not the energy output of the star that matters. It is the energy influx to the planet. If the output of the star is less, the planet just needs to be closer to the star for the influx to be the same.
You're right it's the influx, I shoudn't have said output :roll: . But it does shrink the habital zone greatly.


The energy spectrum might be a problem. Since the output of a M dwarf is mostly IR and red, with little blue and almost no UV, photosynthesis would probably be based on something with a different response curve than chlorophyll.

The spectrum is a problem because there would be a decrease in the amount of energy per photon right (uh, thats what i meant! :D )? If photosynthesis was not based on chlorophyll I doubt Earth life forms (like humans) could adapt to the planet.

Anyway, thanks for clearing that up for me :D

[added] Still the brighness of M type stars is exponentionally smaller (.00006 for Proxima Centauri which is an M5) I still think an M star is an improbable place to find life like ours.

xriso
2003-Apr-05, 07:56 PM
I admit is from a creationist, but you may want to read over it to get some more ideas. His list incorporates necessary characteristics for the galaxy, sun, earth, moon system.

http://www.reasons.org/resources/apologetics/design_evidences/20020502_solar_system_design.shtml?main

Kaptain K
2003-Apr-05, 08:29 PM
I admit is from a creationist, but you may want to read over it to get some more ideas. His list incorporates necessary characteristics for the galaxy, sun, earth, moon system.

http://www.reasons.org/resources/apologetics/design_evidences/20020502_solar_system_design.shtml?main

118 reasons why "we're special". Mostly speculation presented as fact. I didn't read all of them, but I did find one glaring error:

45. Oxygen to nitrogen ratio in atmosphere
1. If larger: advanced life functions would proceed too quickly.
2. If smaller: advanced life functions would proceed too slowly

The oxygen to nitrogen ratio is determined by the presence of life and is, as such, self-regulated by life.

RafaelAustin
2003-Apr-05, 11:09 PM
An interesting read, but I think too many items are reused over and over as well as being over emphasized as critical to life on Earth. I also saw a few items that looked skewed to serve the purpose of the author. And I think the large scale items (galaxy densities, size, etc.) actually help show that the conditions for life are good over most of the universe.

One topic I would like to bring up is on Kuiper Belt Objects affecting the stability of the outer planets. Any opinions? Is their mass enough to help stabilize the solar system?

beskeptical
2003-Apr-06, 05:13 AM
And too add to skeptE56's remark "how close to the star can you get?" What are the chances of having the perfect planet in the very small life zone afforded by a star with such minimal energy.

What do you mean by a 'perfect planet'?

It has been shown recently that what is usually meant by Earth-like conditions are not required for life to arise and evolve.

Re the star requirements: Recent lifeforms have been discovered that do not need solar energy to survive. Bacteria can live on energy derived from chemical reactions rather than photosynthesis. And, higher lifeforms survive by consuming the bacteria. So evolving to complex organisms is possible.

Re a planet that doesn't have a 'perfect orbit or rotation': There can still be habitable zones. Perhaps it is only a narrow band where indirect light falls on a non-rotating planet. Perhaps it would be underground or near volcanic vents. The undersea vents on our planet that support life are not permanant structures yet when new ones form, life arrives to inhabit the area very quickly.

We don't know the scope of habitable conditions just yet. We have a sample size of one planet.

beskeptical
2003-Apr-06, 05:30 AM
I admit is from a creationist, but you may want to read over it to get some more ideas. His list incorporates necessary characteristics for the galaxy, sun, earth, moon system.

http://www.reasons.org/resources/apologetics/design_evidences/20020502_solar_system_design.shtml?main

The link states certain galaxy, solar system, location of solar system, planetary requirements, etc., etc., etc. are needed for advanced life. Even if all those claims of requirements for a habitable planet were true, there are likely to be trillions and trillions of possible planets that meet the criteria. And, as to the claims that whatever led to life on Earth must be necessary for life elsewhere, why would that be true?

Then the bit about we might get primitive life but not life as advanced as humans, again not logical. Say for example you have bacteria dependent on chemical energy. We have evidence then, that higher lifeforms exist by consuming those bacteria.

This is one of those articles that pretends to be scientific, but in reality is more philosophical than scientific.

skeptED56
2003-Apr-06, 06:20 AM
It has been shown recently that what is usually meant by Earth-like conditions are not required for life to arise and evolve.

Re the star requirements: Recent lifeforms have been discovered that do not need solar energy to survive. Bacteria can live on energy derived from chemical reactions rather than photosynthesis. And, higher lifeforms survive by consuming the bacteria. So evolving to complex organisms is possible.

Re a planet that doesn't have a 'perfect orbit or rotation': There can still be habitable zones. Perhaps it is only a narrow band where indirect light falls on a non-rotating planet. Perhaps it would be underground or near volcanic vents. The undersea vents on our planet that support life are not permanant structures yet when new ones form, life arrives to inhabit the area very quickly.

We don't know the scope of habitable conditions just yet. We have a sample size of one planet.

Alot of what we were talking about is refering to neccessary conditions for Earth-like life and life on worlds that could be potentionally colonized. However, life can adapt and evolve in hostile environments. I wouldn't be surprised if life needed planets at all (comets could perhaps evolve life). Would, then, we be able to even recongnize it? Given that we only have a sample size of one planet, life could be more widespread then we thought, or it could be extremely rare, there's only one way to find out for sure right? :D

Vermonter
2003-Apr-06, 02:49 PM
One thing that I have wondered is this: what would this advanced/intelligent life look like? It would have to have appendages and fine manipulators to alter the environment and use tools, most likely upright...I would think that an advanced life would actually look somewhat humanoid.

As for other alternatives to requirements, what if the lifeforms on a planet weren't carbon-based?

Glom
2003-Apr-06, 02:54 PM
Maybe they could have four arms.

skeptED56
2003-Apr-06, 03:00 PM
Alien cephalopods, that would be cool :D

g99
2003-Apr-06, 05:33 PM
I would like to see water living intelegent organisms. Something like a merpeople civilization. That would be really cool.

skeptED56
2003-Apr-06, 09:04 PM
Yes, like how would they adapt and build technologies not based on fire? How would being in an aqautic environment affect their culture? How would the communicate? Awesome :lol:

Glom
2003-Apr-06, 11:02 PM
If the creators of Enterprise are watching... Now's the time to redeem yourselves. If you don't want it, I'm sure the makers of Stargate SG-1 will be happy to do it and competently too.

beskeptical
2003-Apr-07, 09:39 AM
One thing that I have wondered is this: what would this advanced/intelligent life look like? It would have to have appendages and fine manipulators to alter the environment and use tools, most likely upright...I would think that an advanced life would actually look somewhat humanoid.


It is rather amazing, though, how much manipulating elephants can do with their trunks. And, ants do a lot with pinchers. Birds do a lot with feet and beaks. The possibilities are endless.

David Hall
2003-Apr-07, 12:48 PM
Larry Niven's Puppeteers used their mouths as hands (they have two small heads atop long flexible necks), and the ancient Tnuctip were small raccoon-like beings with very dexterous hands.

Niven & Pournelle's Fithp in Footfall are like baby elephants with 8-fingered trunks.

ToSeek
2003-Apr-07, 02:39 PM
One thing that I have wondered is this: what would this advanced/intelligent life look like? It would have to have appendages and fine manipulators to alter the environment and use tools, most likely upright...I would think that an advanced life would actually look somewhat humanoid.


It is rather amazing, though, how much manipulating elephants can do with their trunks. And, ants do a lot with pinchers. Birds do a lot with feet and beaks. The possibilities are endless.

Octopi.*



*Not to be confused with kilopi.

David Hall
2003-Apr-07, 02:51 PM
Octopi.*

*Not to be confused with kilopi.

What are those, seagoing cephalopods with 1000 tentacles?

Donnie B.
2003-Apr-07, 05:25 PM
kilopi: plural form of kilop, per:

kilop (n) (obsolete): fatal, slashing blow in broadsword combat
Pl kilopi > ME kheloup > Lat celopus (two-handed stroke)

-- DB's Dubious Dictionary

logicboy
2003-Apr-07, 05:45 PM
I didn't read every single post so forgive me if I am being redundant.

Life? Intelligent? Microbial?

For intelligent life "Example Humans, well most of us" There needed to be rapid environmental changes in order to promote evolution.

ToSeek
2003-Apr-07, 07:13 PM
kilopi: plural form of kilop, per:

kilop (n) (obsolete): fatal, slashing blow in broadsword combat
Pl kilopi > ME kheloup > Lat celopus (two-handed stroke)

-- DB's Dubious Dictionary

So a certain BABB denizen's posts are analogous to "fatal, slashing blows?" I think I may spend less time on this board....

beskeptical
2003-Apr-07, 08:55 PM
I didn't read every single post so forgive me if I am being redundant.

Life? Intelligent? Microbial?

For intelligent life "Example Humans, well most of us" There needed to be rapid environmental changes in order to promote evolution.

And, if that occurred on Earth, do you have reason to believe it hasn't occurred elsewhere in the Universe? Or, are you just adding to the required ingredient list?

RafaelAustin
2003-Apr-07, 09:27 PM
I'd go along with regular, measured environmental changes. The occasional forest fire has it's evolutionary nich, just the same as a 10km asteroid every few million years. Can anybody restate or quantify that better than me?

logicboy
2003-Apr-08, 02:18 PM
I meant rapid environmental changes for "intelligent" life. I do believe that normal measured changes will cause a species to evolve but not for early humans. What caused them to use fur from other animals as clothing, tools, fire? This wasn't caused by normal changes or else I would think we would have a thick coat of fur ourselves or be more adapted to our environment. The trigger for this must have been a drastic change in our environment.
For example the Dinosaurs had 100s of millions of years to evolve we have had around 65 million years.

snowcelt
2003-Apr-08, 03:59 PM
It seems to me that condition that were not "perfect" for life would be imperfect. Semanics? Perhaps; however, I believe that conditions would have to be at least special. When I had first read abut the snow-ball-earth hypothesis---that 600+ million years ago the earth was shrouded in ice---the authors said that maybe life survived by living around deep sea volcanic vents. Then, conditions changed, the earth thawed out and life radiated outward into other niches. My point being that conditions changed, something special happened to allow this change, without which life would probably still be clinging to volcanic vents. Maybe life can arise in what seems like inhospitible conditions, but then there would be a need for improbable events to occur for far more complex, and finally, intellegent beings to evolve. Impossible? No. But, unlikely? Yes.

Kaptain K
2003-Apr-08, 05:47 PM
...What caused them to use fur from other animals as clothing, tools, fire?...
They expanded into areas and climates for which they were not evolved to survive. They used their intelligence to adapt the environment to them rather than waiting for evolution to adapt them to their environment. :o

kilopi
2003-Apr-10, 06:01 AM
Octopi.*
You know, I hadn't thought about that. I guess if I lost one more finger, I could be an octopi. Right now, I got my fingers in everything.

Good one, Donnie B., especially the "fatal" part. :)

beskeptical
2003-Apr-10, 10:15 AM
While sudden environmental changes do seem to trigger rapid evolutionary changes, so do other events. Disease for example can be the catalyst, or a lifeform invading another habitat. It wouldn't have to be the entire planet that changed for dramatically different species to develop.

Glom
2003-Apr-26, 01:49 AM
It's been established that a cooler main sequence star would have a habitable zone closer to the star to the point that any planet would end up tidal locked.

Question: Could life evolve on a tidally locked planet?

g99
2003-Apr-26, 02:12 AM
It's been established that a cooler main sequence star would have a habitable zone closer to the star to the point that any planet would end up tidal locked.

Question: Could life evolve on a tidally locked planet?

Good question. I suppose that on the fringes of the light and dark side, yes. If there are oceans, i could also assume at the depth of the oceans also on either side.

Now if there is a thick enougth atmosphere, the cycling throught it could keep the far side at a temperture where life could live.
As long as there are pressure differences, you will get wind. Cold air is higher pressure than warm air, so you will see a surface level wind from the dark side towards the sun side. This cold air, will then warm, rise and fall towards the colder side in a cycle. (similar to our atmosphere cycle, but instead of polar, it is equatorial) Of course this is a very simplified system. The real earth system involves three main cycles, but i really down't know how many cycles would be in a system like that on a tiadly locked system.

Added: just thought of this. Would a tidaly locked planet have plate tectonics? I really don't think so, but it might. If not plate tectonics, there would be a big problem with carbon dioxide cycle and other important parts of the atmosphere before life formed.

RafaelAustin
2003-Apr-26, 02:14 AM
That's always been a sticking point with terraforming Venus. Of course that just means it's uninhabitable from our point of view. And if it was truely tidally locked, over a span of millions years, perhaps life could form in the transition areas. But is that even possible? Is the moon 100% locked in its orbit, has the same face always pointed towards us?

tracer
2003-Apr-26, 02:45 AM
Considering the discovery of deep subterranean bacteria in the Earth, and the tantalizing possibility that the first lifeforms on Earth got their "power source" from geothermal heat instead of sunlight -- well, then, being tidally locked or too far from the sun or too close to the sun shouldn't make one whit of difference to the formation of life within a planet's crust, so long as the planet was geologically active.

kilopi
2003-Apr-26, 02:55 AM
well, then, being tidally locked or too far from the sun or too close to the sun shouldn't make one whit of difference to the formation of life within a planet's crust, so long as the planet was geologically active.
Depends. It could make a difference.

Here's my theory. Evolution has often been criticized for violating entropy--there is an organization that violates one of the rules of thermodynamics. Except organization can take place if there is a potential difference from which the organism can extract power to do work on its system. That potential difference is readily available to the organism if its environment changes--hence the need for varying night and day, tide in and tide out. If a planet is locked to the sun, those rapidly varying changes don't occur, and evolution is almost slowed to a stop--it doesn't have time to work before the planet is destroyed.

PS: Asimov's Triple Triumph of the Moon (http://magna.com.au/~prfbrown/i_asimov.html)

TinFoilHat
2003-Apr-26, 03:41 AM
Question: Could life evolve on a tidally locked planet?
No. The part of the planet that never gets any sunlight will become an inescapeable cold trap for volatiles. You'll end up with all the water, and quite possibly all the carbon dioxide, frozen into permament glaciers on the dark side. Liquid water may hand around the terminator for a while, but eventually every molecule will find its way onto a part of the planet that never rises above freezing temperature.

beskeptical
2003-Apr-26, 09:33 AM
Added: just thought of this. Would a tidaly locked planet have plate tectonics? I really don't think so, but it might. If not plate tectonics, there would be a big problem with carbon dioxide cycle and other important parts of the atmosphere before life formed.

I'm not in my area of expertise here but I believe plate tectonics is independent of external gravitational influence. Not that external pull wouldn't impact on plate movement, but the mechanism for plate tectonics is internal heat.

The gravitational pull of Jupiter on Europa produces surface strain and heat. But Earth's crustal plate movements are produced by convection currents within the Earth.

Again, if you assume life can only exist within the limits we are most familiar with on Earth, the evidence supporting this assumption is minimal. Life began on Earth when there was a heavier carbon dioxide atmosphere so we don't need an oxygen atmosphere for life. Life exists around geothermal vents so one doesn't need to be in the so called 'life zone' around a star for a planet to contain living things. Life exists in large quantities within the Earth's crust not just on the surface of the planet.

The possibilities for life will probably surprise us when we eventually do learn the extent they reach.

Glom
2003-Apr-26, 02:56 PM
But Beskeptical, Jupiter and the other Galileans produce tidal forces on Io that generates heat within the inside. AFAIK in this extreme case, the entire crust of Io is a semi-molten mass, but if the tidal forces were not as great, the strain could produce the heat for tectonic movement in the plates. AFAIK, Earth's heat is generated by radioisotopic decay of the crap inside, but it could be generated by tidal strain.

kilopi
2003-Apr-26, 04:01 PM
AFAIK, Earth's heat is generated by radioisotopic decay of the crap inside, but it could be generated by tidal strain.
Neither probably. For the most part, the energy is left over from creation. The radioactive elements are not as concentrated in the core and mantle as in the crust, and tidal strain is relatively small--even at the surface, the strain is only about a meter, and that is the difference between two points 10,000 km apart.

The Galilean moons are a lot smaller than Earth.

daver
2003-Apr-26, 04:37 PM
Question: Could life evolve on a tidally locked planet?
No. The part of the planet that never gets any sunlight will become an inescapeable cold trap for volatiles. You'll end up with all the water, and quite possibly all the carbon dioxide, frozen into permament glaciers on the dark side. Liquid water may hand around the terminator for a while, but eventually every molecule will find its way onto a part of the planet that never rises above freezing temperature.

Maybe for a terrestrial atmosphere. Venus has very little difference in temperature between dayside and nightside as i recall. So for a thick enough atmosphere the cold trap may not be an issue.

daver
2003-Apr-26, 04:42 PM
AFAIK, Earth's heat is generated by radioisotopic decay of the crap inside, but it could be generated by tidal strain.
Neither probably. For the most part, the energy is left over from creation.

Hmm, i haven't crunched through the numbers, but that doesn't seem reasonable to me. I thought Lord Kelven had figured that it would take on the order of tens of thousands of years for the earth to cool off from a molten blob to the tempearture we see today.

kilopi
2003-Apr-26, 04:45 PM
Hmm, i haven't crunched through the numbers, but that doesn't seem reasonable to me. I thought Lord Kelven had figured that it would take on the order of tens of thousands of years for the earth to cool off from a molten blob to the tempearture we see today.
Yep, basing his calculations upon the heat loss we see at the surface--but that is "artificially" inflated by the heat production of radioactive elements in the crust. So, he was assuming that the Earth loses heat a lot faster than it does.

Glom
2003-Apr-26, 04:56 PM
Maybe for a terrestrial atmosphere. Venus has very little difference in temperature between dayside and nightside as i recall. So for a thick enough atmosphere the cold trap may not be an issue.

Crimson mentioned a New Scientist article (http://www.newscientist.com/hottopics/astrobiology/redwilling.jsp) in this thread (http://www.badastronomy.com/phpBB/viewtopic.php?p=78107#78107). It's very good. It says that actually, the atmosphere need not be that thick to atmospheric currents to smoothen out heat differences.

beskeptical
2003-Apr-27, 03:00 AM
But Beskeptical, Jupiter and the other Galileans produce tidal forces on Io that generates heat within the inside. AFAIK in this extreme case, the entire crust of Io is a semi-molten mass, but if the tidal forces were not as great, the strain could produce the heat for tectonic movement in the plates. AFAIK, Earth's heat is generated by radioisotopic decay of the crap inside, but it could be generated by tidal strain.


I am confused by the conversation here. I thought it was being implied that tidal forces were required to have plate tectonics. I don't think that is the case. And, it sounds like Grapes was elborating on the internal source of heat within the Earth in agreement that tidal forces were not required to have plate tectonics.

If I have this wrong, I'm all ears.

tracer
2003-Apr-27, 03:33 AM
Hmm, i haven't crunched through the numbers, but that doesn't seem reasonable to me. I thought Lord Kelven had figured that it would take on the order of tens of thousands of years for the earth to cool off from a molten blob to the tempearture we see today.
Yep, basing his calculations upon the heat loss we see at the surface--but that is "artificially" inflated by the heat production of radioactive elements in the crust. So, he was assuming that the Earth loses heat a lot faster than it does.
Indeed, Kelvin was off by a factor of thousands. It would take a nonradioactive molten Earth closer to 100 million years to cool to the temperature we see today at the crust, and the temperatures we detect today inside the Earth (http://pubs.usgs.gov/gip/interior/).

However, the Earth is over 4 billion years old. Geologists' consensus, as far as I know, is that the core of the Earth, is riddled with heavy radioactive elements that all "fell" down to the center when the Earth was still liquid.

kilopi
2003-Apr-27, 05:14 AM
Indeed, Kelvin was off by a factor of thousands. It would take a nonradioactive molten Earth closer to 100 million years to cool to the temperature we see today at the crust, and the temperatures we detect today inside the Earth (http://pubs.usgs.gov/gip/interior/).
I think 100 million years was right around one of Kelvin's estimates.

Glom
2003-Apr-27, 11:15 AM
I thought it was being implied that tidal forces were required to have plate tectonics.

I wasn't implying it was a requirement, I was saying that tidal stresses can produce heat inside a body that could allow convection currents to drive tectonic activity.

beskeptical
2003-Apr-28, 09:51 AM
Wierd, either my last post went to never never land or I logged out before I hit submit and didn't realize it. I could have sworn I posted that I had misread g99. I had said something to the effect that I misread what g wrote in a melatonin stupor. If anyone finds where I posted that, let me know. :-?

kilopi
2003-Apr-28, 12:35 PM
I had said something to the effect that I misread what g wrote in a melatonin stupor. If anyone finds where I posted that, let me know.
According to the BABB search engine, your use of the word melatonin is the first since David Hall's (http://www.badastronomy.com/phpBB/viewtopic.php?p=38604&highlight=melatonin#38604) last November. BTW, what's a melatonin stupor?

snowcelt
2003-Apr-28, 02:05 PM
I think that there is one thing that we can agree upon which would increase the chances of life happening. A dynamic system. Unfortunitally this does'nt help much because so many planets and moons seem to have this characteristic. And of course, if the planet is dynamic see the first post on this thread. However, if life does arise, and as long as something truely catastrophic does not occur, life would probably hang on for a very long time: or as long as life does'nt hit the threshold of intellegence. Because then that intellegence could destroy itself.

g99
2003-Apr-28, 06:23 PM
Sorry, i haven't read this thread for a while. so catching up with Besceptical:

The earth's internal heat does come mainly from radioactive decay. So if the earth was tidally locked it would still have continentla drift. you are correct with that.

But what if this internal decay was not present? Say the nevulae it formed from has a insignificant amount of these pariticles. Could it then have continental drift?

As glom pointed out, the friction caused by being tidally locked could cause internal heating, as in Jupiter's moons. But would this internal heat be uniform? Would the entire core be heated or only the side facing the sun?

Glom
2003-Apr-28, 08:23 PM
As glom pointed out, the friction caused by being tidally locked could cause internal heating, as in Jupiter's moons. But would this internal heat be uniform? Would the entire core be heated or only the side facing the sun?

I can't remember what I said before, but I'm not sure that a tidally locked planet would experience the same kind of heating as Io or hopefully Europa. While it's rotation is being slowed to tidal lock there would be, but I'm not sure about strain once tidal locked. With Io, it's the pull of Jupiter and other Galileans in all directions that puts the strain on the innards and causes the heating.

kilopi
2003-May-06, 06:01 PM
Sorry, i haven't read this thread for a while. so catching up with Besceptical:

The earth's internal heat does come mainly from radioactive decay. So if the earth was tidally locked it would still have continentla drift. you are correct with that.
It would still have internal heat, but radioactivity is not as important in the core as at the surface. Radioactive elements are more highly concentrated in the crust than in the interior. Still, when I googled on "earth internal heat formation" the first link (http://geollab.jmu.edu/Fichter/PlateTect/heathistory.html) to come up said it was mainly heat of formation aided by radioactivity, whereas the second link (http://newton.dep.anl.gov/askasci/env99/env087.htm)claimed the opposite.

beskeptical
2003-May-06, 09:15 PM
I had said something to the effect that I misread what g wrote in a melatonin stupor. If anyone finds where I posted that, let me know.
According to the BABB search engine, your use of the word melatonin is the first since David Hall's (http://www.badastronomy.com/phpBB/viewtopic.php?p=38604&highlight=melatonin#38604) last November. BTW, what's a melatonin stupor?

Thank you for checking on that for me grapes. I think I logged off before hitting submit.

A melatonin stupor is when your body has indicated it is past your bedtime but your brain is resisting.

David Hall
2003-May-07, 01:35 PM
According to the BABB search engine, your use of the word melatonin is the first since David Hall's (http://www.badastronomy.com/phpBB/viewtopic.php?p=38604&highlight=melatonin#38604) last November.

I've used the word melatonin in a previous post? Well, whadayknow, I guess I did. Strange word that. Not one I'd usually bring up in casual conversation.

And how is it I've overlooked this thread for the last week? I must've been in a melatonin stupor last time I glanced at it. :-)

snowcelt
2003-May-08, 06:37 AM
kilopi wrote:
It would still have internal heat, but radioactivity is not as important in the core as at the surface. Radioactive elements are more highly concentrated in the crust than in the interior. Still, when I googled on "earth internal heat formation" the first link (http://geollab.jmu.edu/Fichter/PlateTect/heathistory.html) to come up said it was mainly heat of formation aided by radioactivity, whereas the second link (http://newton.dep.anl.gov/askasci/env99/env087.htm)claimed the opposite.

It does not matter if the planet is tidally locked. Any planet which has an interior, radioactive element is going to demonstrate surface dynamics... isn't it? I mean, where does the energy go?

John Kierein
2003-May-08, 10:40 AM
When we find life on Europa, we'll see that not all the req'ts are needed. Check this out:
http://www.geocities.com/CapeCanaveral/Galaxy/7827/

kilopi
2003-May-08, 01:16 PM
kilopi wrote:
It would still have internal heat, but radioactivity is not as important in the core as at the surface. Radioactive elements are more highly concentrated in the crust than in the interior. Still, when I googled on "earth internal heat formation" the first link (http://geollab.jmu.edu/Fichter/PlateTect/heathistory.html) to come up said it was mainly heat of formation aided by radioactivity, whereas the second link (http://newton.dep.anl.gov/askasci/env99/env087.htm)claimed the opposite.
It does not matter if the planet is tidally locked. Any planet which has an interior, radioactive element is going to demonstrate surface dynamics... isn't it? I mean, where does the energy go?
Was that comment about tidally locked addressed to me? As to the interior heat, it can dissipate by radiation, conduction, or convection. The first two won't cause tectonic sort of activity, and the third might not. Depends upon the strength of the surface plates.

beskeptical
2003-May-09, 06:35 PM
When we find life on Europa, we'll see that not all the req'ts are needed. Check this out:
http://www.geocities.com/CapeCanaveral/Galaxy/7827/

There's a lot of stuff to weed through there John. The first subject I looked at, whether nanobacteria have indeed been found on Earth, did not lead to supporting evidence in the referrences cited.

http://www.asmusa.org/memonly/asmnews/apr00/topic5.html

Not that I had time yet to go to other cited referrences, but the very first one I went to DID NOT support the conclusions claimed in the original link.

When I have time, I'll check a few more. This is one of those interesting sites that appear scientific by citing lots of referrences. But I am very skeptical of the claims made since it hasn't been in the mainstream science that evidence of life was found in the Allende nor Murchison meteorites. Amino acids, yes, nanobacteria, no.

theperfectjez
2007-Mar-13, 03:42 AM
heya, sorry about the extra late reply, i am doing an essay (see here (http://www.bautforum.com/showthread.php?t=55329)) on the topic, and i was curious as to why you would need water my cometary seeding?

thanks
Jeremy

Noclevername
2007-May-10, 12:56 AM
The oxygen to nitrogen ratio is determined by the presence of life and is, as such, self-regulated by life.

...And has varied over time here on Earth.