[ShredKazoo]

It's incredibly cold in the outer solar system right? So why is it that there is liquid water in these moons? Is it some sort of geothermal heating?

What's the most complex life which could conceivably exist in such a cold environment? Presumably there's very little sunlight penetrating through the ice to the liquid ocean.

[akiselev]

Tidal heating [1]

[1] https://en.m.wikipedia.org/wiki/Tidal_heating

[Aardwolf]

Interesting stuff! Made me find that even rogue planets (free floating without orbiting any star) might theoretically be warm enough to support oceans and life: https://en.wikipedia.org/wiki/Rogue_planet#Warmth

[sanxiyn]

From Earth's hydrothermal vents, we know sunlight isn't necessary for life although energy is.

[Mistletoe]

We don’t know if life started in the light though and then migrated to the vents and adapted. My memory of it is that this is an unanswered question so far.

[peter303]

Its a good hypothesis that life start at deep volcanic vents. Geologist Robert Hazen conducted lab experiments showing that all steps of the metabolic citric cycle occur in this environment without needing catalytic enzymes. Chemical reduction of magma provides the energy. As life developed enzymes to improve metabolism, it could migrate to colder, lower pressure environments.

[wkat4242]

It's also awash with radiation from Jupiter. If there's life, it won't be as we know it :)

[jvanderbot]

Europa is enticing because life would exist under a few km of ice, more than enough to prevent radiation from causing too much problems.

The hydrothermal vents, where the main sources of energy are hypothesized to be, would be deep enough.

[zirgs]

Water is really good at radiation shielding.

[LatteLazy]

Does Jupiter emit any noticeable radiation?