LPSC 2014: Subduction on Europa?
I’m just back from this year’s Lunar and Planetary Conference in Houston, Texas. It was a great meeting, absolutely bursting with fascinating new discoveries and theories spanning the Solar System.
The most exciting for me was some pretty convincing evidence for a system of ice plate tectonics on Jupiter’s moon Europa. We already knew that some process is resurfacing Europa because the density of impact craters on its surface indicates an age of just 40 – 90 million years. It also looks like certain bands on its surfaces are like mid-ocean ridges on the Earth: places where the crust is spreading apart2. So if it is spreading in one place, material needs to be lost elsewhere or Europa would just keep growing. New work by Simon Kattenhorn and Louise Prockter3 seems to have revealed where this is happening: tabular bands. At these bands, there’s a mismatch in the terrain on either side of the band, and when you restore it to its original configuration, you’re left with a gap. There’s not enough topography there for the surface to have simply scrunched up, so it must have subducted down into the ice shell. They have several other strands of evidence, including the suggestive presence of cryolavas on the overriding ‘plate’, just as there is volcanism on the plate above subduction zones on Earth.
Obviously this theory is in its early days, with the full dynamics to be calculated, in particular quantifying whether the density contrast of the surface ice over the material just below it would be enough to cause subduction. But if true, it has exciting astrobiological implications: materials produced by radiolysis at the surface can descend down into the sub-ice ocean and perhaps provide the nutrients necessary for life.
Europa was already looking like Earth’s icy twin in that it has the highest potential for existing life in the Solar System. Now it looks like it’s also the only other body with plate tectonics, a process that has often been cited as a necessary condition for the development of life on Earth. Here’s hoping NASA’s recent positive noises about Europa lead to the voyage of discovery we’re all rooting for!