Surface temperature of a icy rogue planet

A certain imaginary stellar system had once a water world. But instead of evaporating away under the stellar wind, this lucky (or unlucky?) water world (made of only water and a gaseous atmosphere) interacted with a huge gas giant planet and got expelled from its parent stellar system. Now this planet flies away, solitary, without any nearby star.

My question is:

Will the temperature of this planet reach the cosmic background radiation temperature if left alone for long enough? Will it freeze solid? Will its atmosphere turn liquid? Will its atmosphere turn solid?

1. Assume a planet the size of Earth.
2. It is made of almost pure water.
3. Its atmosphere is made out of mostly hydrogen and helium.
4. It has no rocky core.

posted over 9 years ago

Jorge Aldo‭

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