The Ocean of Europa

Europa is the second closest to Jupiter of Galileo’s “Medician Stars”, and one of the four known moons for centuries. Although akin to our Moon in size, it’s covered in ice that is criss-crossed by cracks and blotched with sulphurous looking colours. John Lewis first calculated in the early 1970s that such ice-covered moons would probably have sub-crustal oceans, warmed by the slow trickle of heat from radioactive decay. However when Voyager 1 & 2 flew past, in 1979 & 1980, they discovered that Europa and Io were far warmer than radioactive decay allowed. Io’s volcanism could only be powered by tidal energy from its constant kneading by Jupiter’s gravity. But what of Europa? Close-up views from the Galileo Orbiter revealed what looked like refrozen pack-ice, suggesting an ocean not too far down. But was there enough energy to sustain an ocean just beneath the ice? If so, where was the energy coming from?

A possible answer…

Swirling waters boost chance of life on Europa …from New Scientist Space News

Jupiter Moon Has Violent, Hidden Oceans, Study Suggests …from National Geographic News.

Heating the oceans of distant moons …from ars technica. John Timmer gives good technical details of the article causing all the fuss.

Distant moons may have liquid oceans … from World-Science. Site is sometimes a bit flakey but the article is ok.

The interesting thing comes from the fact the new tidal motions might be causing more rapid processing of oxidisers in the ice. Europa’s ice is energised by the storm of radiation trapped in Jupiter’s magnetic field, and lots of oxygen-rich ice is created, enough to energise any biosphere below… if it can get down there. Perhaps it can.

Catholic Sensibility posted some news on Paul Gilster’s post on Europa’s possible macrofauna… all sparked by an abstract that I reproduce here…

Europa is a prime target for astrobiology. The presence of a global subsurface liquid water ocean and a composition likely to contain a suite of biogenic elements make it a compelling world in the search for a second origin of life. Critical to these factors, however, may be the availability of energy for biological processes on Europa. We have examined the production and availability of oxidants and carbon-containing reductants on Europa to better understand the habitability of the subsurface ocean. Data from the Galileo Near-Infrared Mapping Spectrometer were used to constrain the surface abundance of CO2 to 0.036% by number relative to water. Laboratory results indicate that radiolytically processed CO2-rich ices yield CO and H2CO3; the reductants H2CO, CH3OH, and CH4 are at most minor species. We analyzed chemical sources and sinks and concluded that the radiolytically processed surface of Europa could serve to maintain an oxidized ocean even if the surface oxidants (O2, H2O2, CO2, SO2, and SO4 2?) are delivered only once every 0.5 Gyr. If delivery periods are comparable to the observed surface age (30–70 Myr), then Europa’s ocean could reach O2 concentrations comparable to those found in terrestrial surface waters, even if 109 moles yr?1 of hydrothermally delivered reductants consume most of the oxidant flux. Such an ocean would be energetically hospitable for terrestrial marine macrofauna. The availability of reductants could be the limiting factor for biologically useful chemical energy on Europa.

…note the highlighted sentence. (reference is: Kevin P. Hand, Robert W. Carlson, Christopher F. Chyba. Astrobiology. December 1, 2007, 7(6): 1006-1022. doi:10.1089/ast.2007.0156. found here)