Swirling waters boost chance of life on Europa

by David Shiga for New Scientist

10 December 2008

WITH Jupiter stirring the pot, the planet's icy moon Europa may be brewing a more nutritious soup for life than anyone had expected. Ice-floe-like features on Europa's surface and certain characteristics of its magnetic field suggest there is an ocean of liquid water beneath its surface. The heat needed to keep it liquid has long been thought to be produced by Jupiter's gravity: Europa's distance from the gas giant changes during its orbit, which means the planet's gravitational pull on the moon varies. This stretches and squeezes the moon's rocky core, producing heat by friction. However, new calculations show that additional variations, due to a suspected slight tilt of the moon's spin axis relative to its orbital plane, make it possible for Jupiter's gravity to warm Europa's ocean directly by stirring up currents within it. The heat produced this way could exceed the amount generated by the flexing of Europa's core, according to Robert Tyler of the University of Washington in Seattle (Nature, DOI: 10.1038/nature07571).

If a lot more heat is being generated inside the moon than has been assumed, the icy shell could be thinner than expected: until now estimates of its thickness have ranged from less than 1 kilometre to more than 100 kilometres.If more heat is being generated inside the moon than has been assumed, the icy shell could be thinner than expected A thin shell would be good news for the possibility of life, which would have a tough time surviving without a supply of oxidising chemicals needed for metabolism. These chemicals could be generated on the surface when ultraviolet rays from the sun hit the ice, but would not benefit life unless they could get down into the water through cracks or partial melting of the shell, says Terry Hurford of NASA's Goddard Space Flight Center in Greenbelt, Maryland. "The thinner the ice is, the more likely that the surface can communicate with the ocean," says Hurford. He adds that the effect may also apply to other icy moons, such as Saturn's Enceladus.

[Europa is a great candidate for life in the Solar System. I’m certainly keeping my fingers crossed. With that and the possibility that the methane plumes on Mars might possibly be the result of biological activity, the chances of other life right here in our backyard is definitely looking up.]