Jupiter's moon Europa sports a chilly version of plate tectonics. The icy shell that encases the moon has sections that slide beneath each other in a similar way to Earth's continents and ocean floors. The finding strengthens the notion that Europa could harbour life.
Europa has long been considered one of the best sites in the solar system to search for extraterrestrial life, because it has more water than even Earth does. Its global ocean is encased in a shell of ice 20 to 30 kilometres thick. Rust-coloured lines in the shell are thought to be areas where new ice forms. But this creates a puzzle.
"Nobody thinks Europa is getting bigger," says Francis Nimmo at the University of Southern California, Santa Cruz. So where was all the ice going?
Now, analysis of images from the Galileo spacecraft suggest that large chunks of ice may be returning to the ocean beneath, in the first known instance of tectonics on another world.
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