Posts Tagged ‘Cassini mission’

Oxygen – carbon dioxide atmosphere found on Saturn’s moon Rhea

November 27, 2010

From The New Scientist:

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 anddiscovering 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 Space.com. 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.

These three views of Saturn's moon Rhea from NASA's Cassini spacecraft are enhanced to show colorful splotches and bands on the icy moon's surface. New observations have shown Rhea has an oxygen-rich atmosphere. Credit: NASA/JPL/SSI/LPI

Cassini Finds an Oxygen–Carbon Dioxide Atmosphere at Saturn’s Icy Moon Rhea B. D. Teolis, G. H. Jones, P. F. Miles, R. L. Tokar, B. A. Magee, J. H. Waite, E. Roussos, D. T. Young, F. J. Crary, A. J. Coates, R. E. Johnson, W.-L. Tseng and R. A. Baragiola

Science DOI: 10.1126/science.1198366, Published Online 25 November 2010

Abstract: The flyby measurements of the Cassini spacecraft at Saturn’s moon Rhea reveal a tenuous oxygen–carbon dioxide atmosphere. The atmosphere appears to be sustained by chemical decomposition of the surface water ice under irradiation from Saturn’s magnetospheric plasma. This in situ detection of an oxidizing atmosphere is consistent with remote observations of other icy bodies such as Jupiter’s moons Europa and Ganymede, and suggestive of a reservoir of radiolytic O2 locked within Rhea’s ice. The presence of CO2suggests radiolysis reactions between surface oxidants and organics, or sputtering and/or outgassing of CO2endogenic to Rhea’s ice. Observations of outflowing positive and negative ions give evidence for pickup ionization as a major atmospheric loss mechanism.


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