Thanks to a clue from Greenland, of all places
covered in a rind of water ice perhaps 30 km thick. Beneath the ice lies a salty, globe-girdling ocean that astronomers estimate could be up to 150 km deep. As its larger sister moons—Io, Ganymede and Callisto—pass by in their orbits, their gravity causes Europa to flex slightly, generating interior heat that prevents the water from freezing. Give a warm, salty, amniotic ocean like that a few billion years, and there’s no telling what kind of life it could cook up.
Of all the features that mark Europa’s surface, none are as common as its network of double ridges. Essentially a series of criss-crossing gashes in the moon’s surface each hundreds of miles long, they take the shape of twin ice berms with crests reaching 304 m in height, separated by valleys about 0.8 km wide.
That simple bit of hydrology has big implications for Europa, the authors of the paper concluded. If its double ridges are formed the same way, that means water from the subsurface ocean is forced to the surface there as well, pooling not 30 km deep, but just a kilometer or two within the ice sheet.
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