Conclusion

• Many of the large icy bodies in the outer Solar System are internally differentiated. Thanks largely to tidal heating, some, especially Europa, are likely to have an ocean sandwiched between the icy exterior and the rocky core. Others may have had such an ocean in the past.

• Wherever water rests on warm rock, water must percolate into it and become heated. This will cause hydrothermal convection to begin. Hot, chemical-rich water will emerge at vents, where the resulting local chemical disequilibrium provides an opportunity for living organisms to extract energy by acting as mediators (biological catalysts) for redox reactions.

• If it is true that life on Earth originated at hydrothermal vents, then it is equally likely that life could have become established around similar vents at the 'ice'-rock interface on icy bodies.