There's oxygen on Rhea

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There's oxygen on Rhea

Postby ExplorerAtHeart on Fri Nov 26, 2010 7:37 pm


On its journey around Saturn and its moons, the Cassini mission - jointly run by NASA and the European Space Agency - has made another breathtaking discovery. The findings, published in Science (DOI: 10.1126/science.1198366), show that Rhea, the second biggest moon of the giant planet, has an atmosphere that is 70 per cent oxygen and 30 per cent carbon dioxide. This adds to the picture of Rhea that Cassini has already provided by imaging its craters and discovering its rings.

"This really is the first time that we've seen oxygen directly in the atmosphere of another world", Andrew Coates, from University College London's Mullard Space Science Laboratory, told The Guardian. Layers containing oxygen had already been detected around the Jovian moons Europa and Ganymede in the 1990s, but only from a distance using NASA's Hubble Space Telescope.

This time, Cassini's instrument had the chance to "smell" that oxygen, as it flew through it over Rhea's north pole, just 97 kilometres above the surface, according to the details given on This layer - with an oxygen density probably about 5 trillion times less than on Earth - was "too thin to be remotely detected", said Ben Teolis of the Southwest Research Institute in San Antonio.

So where could this oxygen come from? "As the magnetic field rotates around Saturn, particles carried in the field slam into the hemisphere of Rhea that's facing their flow," Teolis told BBC News. "They hit that hemisphere and break water molecules on the surface. The atoms are then rearranging themselves to make oxygen molecules, which are sputtered from the surface by additional impacting particles." That process is likely to be ongoing, with the oxygen molecules created being constantly whipped out into space.

According to Teolis, "the new results suggest that active, complex chemistry involving oxygen may be quite common throughout the solar system and even our universe". Bad news for alien hunters, though, concludes Wired magazine."All evidence from Cassini indicates Rhea is too cold and devoid of liquid water necessary for life as we know it," Teolis told them.
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