Europa, one of the four largest natural satellites, or moons, orbiting the planet Jupiter, may be the first planetary body in the solar system other than Earth to show evidence of plate tectonics, a research team from the University of Idaho and Johns Hopkins University reported in Nature Geoscience (September 2014). The evidence comes from images sent back from the Galileo spacecraft, which passed Europa 17 times during its orbit of Jupiter between 1995 and 2003. See also: Galileo mission (Jupiter); Galileo observations of Jovian satellites; Jupiter; Satellite (astronomy); Solar system; Space probe
On Earth, plate tectonics balances the creation of new lithosphere at mid-ocean ridges (constructive plate boundaries) and the destruction of older lithosphere at subduction zones (destructive plate boundaries). See also: Lithosphere; Mid-Oceanic Ridge; Plate tectonics; Subduction zones
Europa is entirely covered by water, with an outer surface of solid ice. When the first Galileo images of Europa were analyzed, the initial and most striking observations were how smooth its surface was and how few impact craters were present, indicating that some process was renewing its surface.
Evidence for a tectonic process was found when the research team, examining images of Europa’s surface over time, noticed that a sizable (20,000 km2) part had vanished from view. Further clues suggested that this missing terrain had been subducted under a second plate. Other images also showed evidence of plates sliding past each other. On Earth, this type of lateral plate movement is known as transform faulting. See also: Transform fault
Although the mechanism for creating new surface ice is still unknown, the researchers have said the evidence so far suggests that Europa has a plate tectonic system made up of outer, colder ice plates that move over a warmer ice below.