[zeestephen]

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“How likely is a loose planet to have any atmosphere?”

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Good point.

Interstellar space is about 3 Kelvin, right?

Radiant energy from a nomad planet’s interior would be quite small.

On Earth, for instance, I think it’s less than 1% of what the sun delivers.

[SunkenCiv]

Thanks all.

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

[snip] Mean heat flow is 65 mW/m2 over continental crust and 101 mW/m2 over oceanic crust.[12] This is approximately 1/10 watt/square meter on average, (about 1/10,000 of solar irradiation,)... [/snip]

(1 percent of 1 percent)