Europa’s Poles Have Gone ‘a’ Wanderin’

Posted by Joshua S. Hill

May 16, 2008

Orbiting its much larger parent body Jupiter, Europe is the sixth of at least 63 moons that call the big red planet home, and the smallest of the four Galilean moons. Discovered in 1610 by Galileo Galilei, she was named after a mythical Phoenician noblewoman who was courted by Zeus and became the queen of Crete.

And according to recent research her poles may have been on a long journey towards her equator.

Paul Schenk of the Lunar and Planetary Institute in Houston and his colleagues have been studying imagery from the spacecraft Voyager, Galileo and New Horizon’s, in an attempt to map several arc-shaped depressions spared far apart on Europa.

Measuring in at about 500 kilometers long and with two of them lying exactly on opposite sides of the planet, the depressions are so shallow that, according to Schenk, “you would not notice them if you were walking on Europa.”

Plugging the imagery and data in to a computer model has provided Schenk’s team with what they believe to be proof that the surface scars are the result of a past rotation of the moon’s icy shell, measuring 80°— nearly a quarter-turn.

The theory goes that spinning spheres such as a planet push heavy lumps of material on their surfaces towards their equators. But if a buildup of, in Europa’s case, ice at one of her poles was to occur, it could have sparked what scientists describe as “true polar wander”, or, the movement of a planet’s poles away from their original start positions.

This is an important discovery, because for most planets – such as Mars and Earth – there are large amounts of friction between their internal layers. This makes slippage very slow. But if, for example, an icy crust was resting atop a subsurface ocean, the slippage would be a lot smoother and thus faster.

“We prefer the model of an ice shell moving over an ocean because it is much easier to reorient the shell than the entire body,” said co-author Francis Nimmo of the University of California, Santa Cruz, “and there is a plausible published mechanism for causing the shell to reorient by roughly 90 degrees.”

If indeed there lies underneath the surface a large ocean, than the chance that it also harbors aspects of life increase. And if nothing else, who knows, maybe someone can go and destroy Europa like they’re destroying Earth.

Schenk, Nimmo and Isamu Matsuyama of the Carnegie Institution of Washington (D.C.) report their findings in the May 15 Nature.

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