Europa's Poles May Have Shifted to the Equator

Jupiter's Europa moon is covered by an icy outer shell believed to be housing a global ocean beneath it, where life could exist. New observations on the moon's surface reveal that the icy shell might have shifted as much as 80 degrees in a matter of only 60 million years, supporting the idea that an ocean may indeed lie under the icy crust.

As spheres spin, most of the centrifugal force concentrates towards the equatorial regions. In the case of stars, planets and moons, this leads to the creation of heavy lumps of material at the equator. But, if the material lumps have somehow reached the vicinity of the poles, they can be easily shifted back to the equator. The process is called 'true polar wander'.

For large celestial bodies such as the Earth, this process takes place incredibly slowly due to the high friction generated between the inner layers. But, if the surface crust were to slip across the surface of an ocean, such as in the case of Europa, the 'true polar wander' is greatly accelerated. Paul Schenk from the Lunar and Planetary Institute in Houston, says that deep, curved fractures hundreds of kilometers in length across Europa's surface, seem to indicate that the polar region of the moon tilted 80 degrees towards the equatorial region.

A similar observation has been previously made by Francis Nimmo from the University of California in the case of Saturn's Enceladus, which could also he hiding a liquid ocean beneath its surface.

"We would very much like to find out when it occurred", said Schenk. Although the exact time when the ice sheet on Europa formed is known to be 60 million years ago, scientists cannot yet pinpoint whether or not the 'true polar wander' event happened all at the same time or it spanned over several different events.

Further studies will weigh both possibilities in the months to come and make an estimate of the ice thickness on the Moon, which is now believed to be about 10 kilometers.