Many of the cracks in question look like lines of shallow humps. They resemble the outline of a road paved with back-to-back speed bumps. Other cracks possess the exact same shape, but are flipped over so that they look just like the lines a child makes when drawing the surface of a lake or ocean: a series of short peaks with sloping troughs in between that represent waves.

These cracks are found at all latitudes of the moon such that it looks as if somebody had taken a pencil and drawn humps and troughs all across Europa.

"There is nothing like that in the solar system," said Paul Geissler, a planetary scientist at the University of Arizona's Lunar and Planetary Laboratory. Geissler is a member of the team that has suggested an explanation for the features that involves tidal stresses from a subsurface ocean.

Has worked at various times to find an explanation for Europa's cycloidal features.

"We struggled for a long time with models of plate tectonics," Geissler said. "One early idea was that it was something like the island arcs on Earth where one plate is subducting below another. And it didn't work."

No other explanation has satisfactorily explained the features either, because the repeating chains arc-shaped ridges are so different from other cracks on Europa, or anywhere else on the solar system.