Year in review: Tectonics active on Europa

A frozen world hundreds of millions of kilometers away is starting to look a bit like home. This year researchers discovered active plate tectonics reshaping the surface of Jupiter’s icy moon Europa. The finding marks the first evidence of active plate tectonics on another world (SN: 10/4/14, p. 10).

The researchers made the discovery while scrutinizing an area of Europa’s surface mapped by NASA’s Galileo spacecraft in 1998. In the moon’s northern hemisphere, a hunk of landscape the size of New Jersey had vanished. Like a torn photograph placed so the pieces overlap, Europa’s crisscrossing surface fractures didn’t properly line up. The researchers propose that this missing region dived beneath other ice layers in a process analogous to subduction on Earth, in which one tectonic plate slides beneath another.

Europa’s surface is broken into a mosaic of these shifting ice slabs, the researchers suggest. If the subduction rate is similar to Earth’s, the moon’s entire surface could recycle itself in less than 90 million years, says planetary scientist Simon Kattenhorn of the University of Idaho in Moscow. This periodic renewal could explain Europa’s unusually young surface. Even though Europa formed more than 4 billion years ago, its icy surface appears to be only about 40 million to 90 million years old.

The blending of exterior and interior ice could benefit any life lurking in the moon’s subsurface ocean, Kattenhorn says. Radiation from Jupiter could spark formation of energy-packed organic nutrients from simpler chemicals on Europa’s outer shell. The tectonic blending offers a way for such surface nutrients to cycle into the liquid ocean below. “These geological cycles could be partially responsible for powering a biosphere,” says astrobiologist Britney Schmidt of Georgia Tech in Atlanta.

The finding comes at an opportune time. NASA’s proposed Europa Clipper mission recently entered early design stages in preparation for a 2022 launch. In July, NASA asked scientists to send ideas for instruments for the mission. The agency plans to choose which ideas to develop next April.