Surface of Europa

Europa is the biggest ice rink in the Solar System – a moon of Jupiter so smooth that, from a distance, it looks exactly like a snooker cue ball. Close up, however, curious linear markings appear. This enhanced image, taken by NASA’s Galileo orbiter, reveals cracks in the moon’s ice, caused by warm liquid welling up from below. For ten kilometres below the ice is believed to be the biggest ocean in the Solar System, perhaps as much as 100 kilometres deep.

In his novel 2010: Odyssey 2 Arthur C Clarke, whose books were based on hard science, speculated about the possiblity that Europa might sustain life because of a discovery made in 1977. Deep down on the Earth’s ocean floor, a team led by Robert Ballard found mineral-rich, super-hot water erupting from “hydrothermal vents”. Around each vent was an ecosystem of sulphur-eating bacteria and arm-length “tube worms”. If life can thrive like this in total darkness, the argument goes, then why not in the blackness beneath the ice of Europa?