I find the concept of interstellar planets interesting. They'd make convenient way-stations if we ever were able to travel beyond the solar system, assuming any just happened to be along the way.

I've read that it's possible life could exist on such worlds, that dense atmospheres and/or volcanoes could provide the heat required to support it. Of course this would be life that required no sunlight whatsoever.

It is said that planets like this would lack weather due to the lack of a sun. Which leaves me wondering how much longer it might take life to evolve in such a place without the dynamic chaotic environment that weather provides. It seems more likely that if life was ever found in such a place it might have started first while the planet was in orbit in a solar system and hung on tight while whatever catastrophe occurred that flung it out to wander aimlessly among the stars.

I'm curious to know if anyone knows of any processes that would occur on such a world that would provide a chaotic enough environment that life could spontaneously form. It seems that waiting on geologic processes might take a very long time.

__________________
The only way of finding the limits of the possible is by going beyond them into the impossible.

Arthur C. Clarke

The Brain Science Podcast

As far as we know, life doesn't need a dynamic, chaotic environment provided by wheather to develop or evolve. We don't know if stability or change is most helpful in the development of self replicators. It is quite possible that life tends to first form underground, which makes wheather rather irrelevant.

I have no way of proving this because despite all attempts with kitchen chemicals I have yet to create life, but it seems to me that some degree of chaos would be involved to sort through the myriad chemical combinations required to create self-replicating molecules. And then once that occurred, some level of additional chaos would be required to create conditions conducive to evolutionary processes.

For instance, if a self-replicating molecule formed in some primordial soup that did no harm to the self-replicator then there would be no selection process. So it seems there would have to be a range of conditions to which the molecules were subjected that would alternately support then not support the molecule's ability to replicate and then the changes would occur that would allow random molecular mutations to be selected for fitness.

It just seems to make sense to me that some chaotic processes must occur to continuously shuffle through the possibilities. However, I am open to hearing alternative ideas.

__________________
The only way of finding the limits of the possible is by going beyond them into the impossible.

Arthur C. Clarke

The Brain Science Podcast

The chaos to which you are referring doesn't require wheather.

And how would you know if you've managed to create life or not in your experiments with kitchen stuff? It can be what we scientists call very very small.

Much too small to make off with say, a whole leg.

the magic ingredient to making life is, Barry White. RNA spontaneously forms to his hits.

If not weather, then what is required and how can that occur on a interstellar planet?

__________________
The only way of finding the limits of the possible is by going beyond them into the impossible.

Arthur C. Clarke

The Brain Science Podcast

We don't know what's required. But plenty of people have made suggestions, and there is no particular reason at the moment to believe that there is only one path that leads to self replicating molecules.

This Wikipedia article lists several posibilities:

http://en.wikipedia.org/wiki/Origin_of_life

If life on such a planet is not impossible, it's mighty close to impossible. Pluto is hardly "interstellar", and it has a surface temperature about 50 Kelvins (-223 C, -369 F). A larger planet, like Earth, would surely retain internal heat a lot longer, and even after a few billion years, still probably not be quite that cold, at Pluto's distance from the sun. Still, the globally averaged heat flow of Earth is miniscule compared to solar input.

An interstellar planet must have started out near a star, but except perhaps near a thermal vent, its surface would be frozen solid, and so would any atmosphere it once had. If life had a chance to start while the planet was still "stellar", it might cling at such places, but I doubt it. Certainly, if life had not already started, it would never start under such unfavorable conditions.

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David J Stevenson's paper Possibility of life-sustaining planets in interstellar space (pdf) describes one possibility: the retention of a dense hydrogen atmosphere with a high infra-red opacity, which maintains the planet's surface temperature above the freezing point of water, from internal radioactive heating alone.

Grant Hutchison

If the earth were somehow flung deep into interstellar space, bacteria in the crust would continue to go on living for billions of years, so life is not in such a precarious position on such a world, and for all we know, life started underground. As Grant has mentioned, a strong greenhouse atmosphere could keep the surface of a rouge planet warm as well.

It is interesting you turned up Stevenson's paper. That is what led me to think about this stuff in the first place.

I will grant the probability of life forming on an interstellar planet is minuscule but it seems it may not be impossible under certain conditions. I just think that perhaps the chances aren't quite as good as Stevenson so optimistically states.

It seems unlikely such a planet would have a moon, but if it did it could go a long way toward helping produce and sustaining life. It would help by generating heat through tidal forces, helping stir the oceans, and possibly creating more weather variations. I imagine a planet with no sun as having stagnant oceans, very little weather, and slow dynamic processes that might not stir things up enough to create life.

At least with a moon the core may not cool as quickly as it would without one, and that extra time may make a difference.

__________________
The only way of finding the limits of the possible is by going beyond them into the impossible.

Arthur C. Clarke

The Brain Science Podcast

Gas giants and be flung out of solar systems and it's possible for their moons to survive this process. They could be tidally heated with an interior ocean like Europa, or could have surface liquid water.

I'm not really sure what you mean. I'm supposing English isn't your first language so I'm just looking for clarification.

While the theory states rogue planets could occur by being flung from a solar system by a gas giant, it also states that it could grow in interstellar gas as well, and I would imagine that a moon might be more probable in that situation than in one where the planet was sling-shotted by a playful Jupiter.

__________________
The only way of finding the limits of the possible is by going beyond them into the impossible.

Arthur C. Clarke

The Brain Science Podcast

It is possible for a gas giant to be ejected from a solar system (most likely due to interaction with another gas giant) without losing all its moons. Gas giants plus moons could also form without a star.

Do you suppose that under similar circumstances a planet could swipe a moon from a gas giant that is flinging it?

__________________
The only way of finding the limits of the possible is by going beyond them into the impossible.

Arthur C. Clarke

The Brain Science Podcast

I think it's possible, especially for planets slightly greater than Earth-mass. However, without any "free" energy from sunlight, limiting life's options to anaerobic and/or chemosynthetic reactions, I'm guessing the biosphere would be very sluggish and energy-poor.

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"Call me old-fashioned, but I think fire is magic. And it scares me a lot."

--The State

I think so.

Are the lifeforms near ocean vents using anaerobic respiration or chemosynthetic reactions or are they benefiting from a planet bathed in sunlight in an indirect fashion such as fallen detritus and oxygen derived from photosynthesis across the globe? Are they really on some kind of independent system down there or does that system rely upon normal life cycles elsewhere?

__________________
The only way of finding the limits of the possible is by going beyond them into the impossible.

Arthur C. Clarke

The Brain Science Podcast

^
A little of both, IIRC.

__________________
"Call me old-fashioned, but I think fire is magic. And it scares me a lot."

--The State