Washington - The corrugated shape of the surface of Jupiter's moon Europa may be caused by tidal forces pulling against the frozen cap of a deep ocean of water, US researchers say.
A computer model created by astronomers at the University of Arizona at Tucson suggests that the fissures and ridges that run for hundreds of miles across the surface near Europa's south pole are caused by the gravity tug of Jupiter as the moon circles the giant planet.
The fractured surface features have puzzled astronomers since they were first discovered in pictures taken by the Voyager spacecraft in 1979.
Other studies have suggested that Europa, one of Jupiter's four moons, has a 160km deep ocean with a frozen surface. But the research didn't explain the formation of a strange pattern of cracks and fractures, called cycloidal features, distributed over the moon.
In a study appearing Friday in the journal Science, Gregory V Hoppa, B Randall Tufts, Richard Greenberg and Paul E Geissler of the University of Arizona say they now have the answer.
A computer program that models the effect of Jupiter's gravity on the surface of Europa shows that as the small moon orbits its giant planet the frozen surface would repeatedly crack and refreeze.
The cracks form in cycles that are consistent with the three-and-a-half day, oval-shaped orbit of Europa around Jupiter, the researchers say. Tidal forces on Europa, caused by the gravitational tug of Jupiter, are highest when the moon is closest to the planet. The effects diminish as the moon moves farther away.
The extreme Europa tides cause the ice to flex, crack, reform, and then crack again, an endless cycle that leaves a frozen pattern in the surface ice, the researchers say. - Sapa-AP