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Comment by hartror | Hacker News Reader

The beauty of this is geothermal heat adds the opportunity for life to develop/survive outside the Goldilocks Zone [1]. Not just in our solar system where the moons of Jupiter and Saturn are very active geologically due to tidal forces [2] but on extrasolar moons and planets that otherwise may not be suited to life.

Perhaps there is more life in the universe where the base energy source is that of geothermal than that of radiation from a star? I wonder what an sentient life form evolved from this environment would be like?

I feel a short story coming on.

[1] http://en.wikipedia.org/wiki/Habitable_zone

[2] http://en.wikipedia.org/wiki/Tidal_force

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It's funny that this is coming up now - just this week, there was a pre-print on arxiv.org that explored the possibility of a planet being heated (possibly enough to become habitable) by dark matter annihilation in its core: http://arxiv.org/abs/1103.5086

The long term stability of such a heat source is poor (it would start very hot, then cool exponentially). But it's an interesting idea.

You do realize that exponential decay actually translates to always-declining but relatively stable behavior as you approach the limit, right?

How long is long term though? If I'm reading this right, the highest generator of heat is naturally radioactive thorium, which has a half-life of about 14 billion years. The Earth is only about 4.54 billion years old.

No, thorium is the lowest, not the highest. It decays too slowly to be a large source of heat.

Potassium-40 (1.2 billion years) is the highest.

The article says that thorium releases 3.27×10^-12 Watts of heat per kg of mantle, while potassium releases 1.08×10^-12 Watts.

Isn't that more, or do I just fail at basic math?

I got my info from here: http://www.berkeley.edu/news/media/releases/2003/12/10_heat.... which said potassium. Shrug.

It would be interesting to determine how much of the dark side of the Earth is heated by leftover warmth from the daylight, and how much is geothermal.

My guess is that geothermal contributes almost nothing. I wouldn't be surprised if the solar radiation via a full moon contributes more than geothermal.

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