False color image of Saturn's moon Dione
 (Credit: NASA/JPL/Space Science Institute)
NASA’s Cassini probe, which is currently on a mission to explore Saturn and her moons, has detected signs of a thin atmosphere around Saturn’s moon Dione. This confirms a hypothesis from the Hubble Space Telescope, which detected signs of ozone around that Moon.

The Cassini probe detected a very thin concentration of oxygen ions around the moon – one ion for every 11 cubic centimeters of space around the Moon. That’s roughly the same density as the Earth’s atmosphere 300 miles above its surface. That’s actually higher above the Earth than the International Space Station, which maintains an altitude between about 205 and 255 miles.

Dione isn’t the only one of Saturn’s moons that has an atmosphere. Titan has a much denser atmosphere, and the moon Rhea also has a thin, oxygen atmosphere comparable to Dione’s. It’s not certain exactly how the oxygen molecules are created in those moons’ atmsopheres, but this finding does demonstrate that oxygen atmospheres are possible without being the product of life.

The most likely culprit for the creation of the oxygen molecules are radioactive particles from the Sun or other sources striking the water-ice on Dione’s surface. That could cause the oxygen to become liberated from water molecule and turned into a gaseous form.

“Scientists weren’t even sure Dione would be big enough to hang on to an exosphere, but this new research shows that Dione is even more interesting than we previously thought,” said Amanda Hendrix, Cassini deputy project scientist in a NASA press release. “Scientists are now digging through Cassini data on Dione to look at this moon in more detail.”

Now that the presence of oxygen ions have been detected around Dione, the next step is for Cassini project scientists to examine Cassini’s data from its flyby last December. It’ll be interesting to see what they find, if anything.

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