WITH Jupiter stirring the pot, the planet鈥檚 icy moon Europa may be brewing a more nutritious soup for life than anyone had expected.
Ice-floe-like features on Europa鈥檚 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鈥檚 gravity: Europa鈥檚 distance from the gas giant changes during its orbit, which means the planet鈥檚 gravitational pull on the moon varies. This stretches and squeezes the moon鈥檚 rocky core, producing heat by friction.
However, new calculations show that additional variations, due to a suspected slight tilt of the moon鈥檚 spin axis relative to its orbital plane, make it possible for Jupiter鈥檚 gravity to warm Europa鈥檚 ocean directly by stirring up currents within it. The heat produced this way could exceed the amount generated by the flexing of Europa鈥檚 core, according to Robert Tyler of the University of Washington in Seattle (Nature, ).
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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.
鈥淚f more heat is being generated inside the moon than has been assumed, the icy shell could be thinner than expected鈥�
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 fast-moving charged particles trapped in Jupiter鈥檚 extensive magnetic field hit the ice on Europa. But they 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鈥檚 Goddard Space Flight Center in Greenbelt, Maryland.
鈥淭he thinner the ice is, the more likely that the surface can communicate with the ocean,鈥� says Hurford. He adds that the effect may also apply to other icy moons, such as Saturn鈥檚 Enceladus.
