Deep and Dark

Abstract

Europa is on everyone’s short list of destinations for finding life in the Solar System beyond Earth. This is because water is found there in abundance, almost surely in liquid form, protected from the harshness of space by a thick layer of ice. But the ice is restless, cracking continually and moving about in rafts and slabs that reflect the push and pull of gravity from Europa’s huge parent, Jupiter, and its larger nearby siblings, the moons of Io, Ganymede, and Callisto. And gravitational flexing is only the start of the story. There’s a tenuous atmosphere of oxygen, fed by the sputtering impact of Jupiter’s powerful stream of radiation that splits the water molecules at the surface into their constituent hydrogen and oxygen atoms. A slight distortion of Jupiter’s electromagnetic field at Europa suggests the presence there of either a metallic core, or a salty ocean beneath the ice, or both, that rotate at different rates (asynchronously) from the planetoid’s surface. This could mean either a source of internal heating from radioactive decay in the core, or strong global currents of water, or both. Combine that with the possibility that thermal vents at the bottom of Europa’s deep ocean and emissions of compounds like hydrogen sulfide and organic molecules like methane from the mantle could provide more energy options as well as the building blocks for polymeric chemistry, and all the requisites for life are at hand.