A photo-montage of Galileo's new Europa images set onto a picture taken by Voyager in 1979. Though this 'buried' ocean has long been scientists' and science-fiction writers' favourite candidate for extraterrestrial life, it is probably too dark to support complex photosynthetic organisms 1 . But now researchers propose a new model for the formation of Europa's surface ridges in which photosynthetic life on this jovian moon 2 might just get a look in.
Debate is intense, ideas are plentiful, and direct data are scarce.
They suggest that tidal forces due to Jupiter's gravity make planes of ice flow across each other in narrow zones. One implication of this latest model would be the continual creation of small pockets of salty water by tidal frictional melting. Impurities like salts would also help by lowering the melting point. Frozen bacteria thawing out in a meltwater pocket near the surface of the ice crust, in reach of dim sunlight, might then have a chance to grow. Gaidos and Nimmo estimate however that a melted water pocket, quickly losing heat through the surrounding ice, could last only a few tens of years.