The icy outer shell of Jupiter鈥檚 moon Europa may have slipped about 80掳 within the last 60 million years, carrying the moon鈥檚 polar regions towards its equator, a new study reports. The research bolsters the idea that a global ocean 鈥� which just might harbour life 鈥� lies hidden beneath the moon鈥檚 icy surface.
Spinning spheres push heavy lumps on their surfaces towards their equators. If the lumps lie near the poles, they can slip away from the spin axis in a process called 鈥榯rue polar wander鈥�.
For large bodies with friction between their internal layers, such as the Earth and Mars, such slippage can be very slow. But an icy outer crust could tilt much faster if it floated on a subsurface ocean.
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That is what Paul Schenk of the Lunar and Planetary Institute in Houston, Texas, US, and colleagues believe happened on Europa, whose fractured, icy surface has long hinted at an underlying ocean.
The researchers say three deep troughs that curve hundreds of kilometres across the moon match strains expected by tilting the polar regions 80掳 towards the equator. Team member Francis Nimmo of the University of California, Santa Cruz, has previously suggested that Saturn鈥檚 moon Enceladus, which may have a subsurface ocean, tilted over in the past.
But some questions remain about the possibility that Europa鈥檚 crust rolled over, and the researchers will try to answer them over the coming months.
鈥淲e would very much like to find out when it occurred,鈥� Schenk told New 杏吧原创. Studies suggest Europa鈥檚 icy surface formed 60 million years ago, but the team has yet to determine if the slip happened all at once or in a series of events.
They also hope to better pin down the thickness of the ice, which is now estimated at about 10 kilometres.
Journal reference: (vol 453, p 368)
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