SATURN'S tiny moon Enceladus is brimming with liquid water and cannot be ruled out as a distant outpost of life.
Last year NASA's Cassini spacecraft sent back images of the moon, which is only 500 kilometres across, showing geysers of ice particles and water vapour spewing out of the south polar region. Researchers think that the most likely source is liquid water boiling off from reservoirs near the surface. No one yet knows what energy source is keeping the water in its liquid state (Science, vol 311, p 1399).
The decay of radioactive elements in the moon's rocky core could not, on its own, generate sufficient heat. An insulating shell of clathrate hydrates - a form of water ice containing trapped gas molecules - could help Enceladus retain more heat, and additional warming may come from the gravitational tug of war between Enceladus and Dione, a neighbouring moon. Cassini also recorded traces of acetylene and propane in the plumes, suggesting that organic compounds are present, too.
"If we had done nothing else, these findings alone would have made the Cassini mission worthwhile," says imaging team leader Carolyn Porco of the Space Science Institute in Boulder, Colorado. A chance to learn more will come during Cassini's next pass by Enceladus, scheduled for 2008, but looking for life will be a job for a future mission.
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18:53 05 September 2008
