Hydrothermal Systems on Europa

There is mounting evidence for a deep ( ∼ 100 km) ocean beneath Europa's icy outer shell. This ocean is maintained by heating that results from tidal interactions between Europa and Jupiter. If the global tidal heat flux of ∼ 8.7 x 10¹² Watts enters the base of the ocean through its rocky crust an average thermal gradient of approximately 150° C/km is expected. Such a high thermal gradient, coupled with localized magmatism and crustal deformation is likely to generate enough rock permeability to maintain active hydrothermal circulation through the Europan crust. In analogy with hydrothermal activity beneath the seafloor on Earth, we assume that crustal permeability is similar to that estimated at mid-ocean ridges, that hydrothermal fluids would reach similar temperatures ( ∼ 300-400° C), and that hydrothermal activity accounts for 1/2 of the crustal heat loss. The major difference between hydrothermal activity on Europa and on Earth would then stem from the large differences in gravitational acceleration between the two bodies (1.31 m/s² on Europa versus 9.8 m/s² on Earth). As a result of the low gravitational acceleration on Europa, buoyancy driven hydrothermal flow would be nearly an order of magnitude smaller than on Earth, all other factors being equal. Consequently, the heat transported by Europan hydrothermal systems would typically be significantly less than their Earthly counterparts. Since the total hydrothermal heat flux on Europa and on Earth are within a factor of two, hydrothermal activity on Europa is likely characterized by more numerous, but lower heat flux systems. How this style of high-temperature hydrothermal activity affects ocean circulation, melt through events, planetary resurfacing, and the evolution of life needs to be further considered.