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On Earth, there are geothermal vents - heat coming from underground vents that support life at the bottom of the ocean where the sun cannot reach.

My question is, would this be possible to support life in the atmosphere of a planet as the only source of heat? I'm thinking of a planet with these vents dotted around the surface like oases, each one surrounded by teeming life (even if it's just basic vegetation or very simple animal life) in an otherwise cold and barren landscape.

Further to this, could they support a small communities? People didn't necessarily evolve there (perhaps space-travelling colonists crash-landed there or something).

There are one or more stars close enough to provide a twilight level of light but no heat. (Think outer planets) though the people, while as close to being human as possible, may have somehow superior or different vision to ours (e.g. different visible frequencies) so they'd be able to see just fine. The atmosphere would have a safe level of oxygen & other gasses so it could be breathed by human-like creatures and the indigenous life.

My question is, is this possible? What are the major drawbacks to this that would make it implausible and how can they be overcome (naturally, not with technology)?

e.g. ...

  • Would the planet's depths too quickly run out of heat as to support meaningful life on the planet? If so, how could it be "refueled" (e.g. frequent meteor impacts)?
  • Would the heat just dissipate into the rest of the atmosphere and
    become too thinly spread to support life? What natural forces could
    cause it to stay localised?
  • Would travel between the vents be possible without space-suits (like could the oxygen exist as a gas in the low temperatures between vents)?

What else?

EDIT

Been thinking about this a bit more... My idea is to have just warm spots around the planet rather than the whole planet warmed by the vents. Could it work if the vents (at least the habitable ones) were at the bottom of deep craters in the ground? The idea is that the atmosphere fills in the craters, but is not really thick enough to extend above them. This way, no heat is lost through convection.

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    $\begingroup$ This is actually what is happening in hydrothermal vents. Nuclear decay is what heats the planet continuously, so that the core remains hot. $\endgroup$
    – Lacklub
    Apr 22, 2016 at 13:11
  • $\begingroup$ My answer on this question re: Habitibility of an icy volcano is very similar to how I would answer this question. The only difference is major component of heating vs. nearly all heating. Assuming major component means 51%, the end result would be the same. I thought about marking this as a duplicate question, but decided against it as there are some differences. $\endgroup$
    – Gary Walker
    Apr 23, 2016 at 0:11

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There are, unfortunately, few real-world phenomena with which to compare this hypothetical scenario, but I'll do my best.

First we need to build our hypothetical planet. It will need a few things:

  • Volcanism, to generate the thermal vents
  • Atmosphere, to provide some sort of thermal insulation
  • Magnetosphere, to protect the inhabitants

Examining planets in our solar system we seem to come up short, except the Earth. However, if we examine moons in our solar system, we might have something. No one lunar body possesses all these criteria, but there are examples that have one or more each.

  • Io, a moon of Jupiter, is extremely volcanic. The massive tidal forces involved with anything concerning Jupiter literally squeeze Io as it rotates, generating immense heat. Io does not have a magnetosphere of its own, but it does have protection from Jupiter's magnetosphere. Unfortunately Io has little-to-no atmosphere whatsoever.
  • Titan, a moon of Saturn, has a dense atmosphere of mostly Nitrogen. It has more atmospheric pressure than even the Earth. The moon also has volcanism of a sort, in the form of Cryovolcanos (which are so damn cool). These volcanos are not hot, but they exist. Titan does NOT have a magnetosphere.
  • Ganymede, the largest moon of Jupiter, and largest lunar body in the solar system, has very little atmosphere (more than Io, but far less than Titan), a small but insignificant amount of volcanism, but it DOES have its own magnetosphere, something no other moon has.

So we know all of our needed features are possible, we just need to combine them into a single planet. It would unfortunately have to remain a moon of a massive gas giant in order to produce the geological heating, but I don't think this can be helped. The thick atmosphere would help keep the heat of the volcanos and thermal vents on the surface of the moon, and the magnetosphere of the moon combined with the magnetosphere of its mother planet would be enough to protect the inhabitants from solar winds, should there be any.

Not sure if this would suffice for your scenario, but it's the best I got.

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  • $\begingroup$ "It would unfortunately have to remain a moon of a massive gas giant in order to produce the geological heating" - Why? If Earth can do it? $\endgroup$
    – komodosp
    Apr 25, 2016 at 8:28
  • $\begingroup$ @colmde I'm somewhat ashamed to say I hadn't even considered the Earth as I answered your question, but you are quite right. I don't think the Earth's atmosphere is substantial enough to trap enough geothermal heat to sustain life, but we are quite volcanic (an atmosphere like Venus might work). I do believe the tidal forces of our larger-than-usual moon are responsible for the geological activity, though, so your hypothetical planet may still need some sort of partner to provide these tidal forces. $\endgroup$
    – MozerShmozer
    Apr 25, 2016 at 15:23

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