A subject of much speculation, distinctive sets of parallel ridges mark the icy crust of Europa, Jupiter’s smallest moon. Researchers now claim that the ridges’ formation mechanism mirrors that of a strikingly similar pair on Greenland’s ice sheet. There, surface water seeped through fissures in the sheet and formed a water pocket that subsequently disrupted the overlying ice, forcing fragments of it upward and outward into peaks, as the pocket froze and expanded. Although Europa lacks liquid surface water, the same process could be driven by the moon’s subsurface ocean.

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