Ocean found beneath ice of Saturn moon

Last updated 14:39 04/04/2014
Enceladus
Nasa
UNDERGROUND OCEAN: This illustration shows the possible interior Enceladus - an icy outer shell and a low density, rocky core with an ocean sandwiched in between the two.

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Scientists have uncovered a vast ocean beneath the icy surface of Saturn's little moon Enceladus.

Italian and American researchers made the discovery using Cassini, a Nasa-European spacecraft still exploring Saturn and its rings 17 years after its launch from Cape Canaveral.

This new ocean of liquid water - as big as or even bigger than North America's Lake Superior - is centred at the south pole of Enceladus and could encompass much if not most of the moon. Enceladus is about 499 kilometres in diameter.

The data does not indicate if the ocean extends to the north pole, said the lead researcher, Luciano Iess of Sapienza University of Rome. At the very least, it's a regional sea some 40 kilometres deep under kilometres-thick ice.

Cassini's rudimentary instruments also cannot determine whether the moon's ocean harbours any form of life. Another mission using more sophisticated instruments is needed to make that search.

This latest discovery makes the interior of Enceladus "a very attractive potential place to look for life", said Cornell University planetary scientist Jonathan Lunine, who took part in the study.

In 2005, Cassini detected a plume streaming from cracks in the south polar region. Scientists suspected these jets of salty water vapour and ice - containing molecules such as methane - might come from a subsurface ocean. On Thursday, they confirmed its presence. Their findings appear in the journal Science.

Cassini provided gravity measurements from three close fly-bys of Enceladus from 2010 to 2012. Data indicated a dense material beneath the surface of the south pole, most likely liquid water.

The ocean is believed to be sandwiched between kilometres of surface ice and a rocky core.

"It's extraordinary what Cassini has been able to do for this small moon," said California Institute of Technology's David Stevenson, part of the research team. But "this is not like mapping the surface of the Earth or mapping the surface of the moon, it's nothing like that. It's much cruder, and it's amazing that we've been able to do as much as we can."

Enceladus is not the only moon in the solar system believed to have a subsurface sea.

Titan, the largest of Saturn's dozens of moons, is believed to have a global ocean. Evidence also points to oceans inside the giant Jupiter moons of Callisto and Ganymede. And Jupiter's Europa also has a hidden reservoir similar to that of Enceladus, complete with plumes and a rocky bottom.

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Cassini, already exceeding its life expectancy, is to make three more fly-bys of Enceladus before the mission ends in 2017.

- AP

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