Europa: New horizons for Astrobiology

Abstract

Europa is the smallest of the Galilean satellites of Jupiter, although it is however a remarkable body and the primary focus of astrobiological interest in the Jovian system. Geological and magnetic evidences, as well as theoretical considerations, strongly suggest that Europa has a thin ice shell, maybe a few kilometers or a few tens of kilometers thick, which floats on an internal ocean of liquid water. Some anomalies have been observed in the huge magnetic field of Jupiter whenever Europa goes through it, which seems to indicate that this ocean is made of conductive water, due to a probable high content of salts. Moreover,the low density of impact craters suggest an surface age of about 60 Myr in average, which is very young in geological terms, indicating that internal activity, driven by tidal heating, is resurfacing the moon at the present time. So, Europa shows an overprint of crisscrossing ridges and linear markings, some extending for thousand of kilometers, which are locally disrupted for chaotic terrains, building a colorful and exotic textured surface. All of these features make of Europa a theoretically good niche for life. Biological organisms might exist in the salty internal ocean, in the icy shell (active or latent) at places such as fractures, veins or liquid reservoirs, on the internal sea floor in hydrothermal vents or submarine volcanoes, or even within the rocky interior.