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Cassini Search Finds No Europa Atmospheric Plumes

Dec. 18, 2014
Tucson, Ariz. -- Recent analysis of data collected by NASA’s Cassini spacecraft during its 2001 flyby of Jupiter sheds new light on the atmosphere of the planet’s moon Europa.
Results show that recently discovered gas plumes on Europa do not contribute to the thin atmosphere, said PSI Senior Scientist Amanda Hendrix, a co-author on a paper titled “A New Understanding of the Europa Atmosphere and Limits on Geophysical Activity” that appears in The Astrophysical Journal. Paper results are being presented today at the American Geophysical Union fall meeting in San Francisco.
 “It is certainly possible – even likely – that plume activity occurs, but that it is sporadic. If eruptive activity was occurring at the time of Cassini’s flyby, it was at a level too low to be detectable by UVIS,” Hendrix said. 
Hendrix specializes in UV spectroscopy of surfaces and thin atmospheres. She has studied Europa using data from NASA’s Galileo spacecraft and Earth-based measurements, as well as investigating Saturn’s active moon Enceladus, helping to put the Cassini results into perspective.
PSI Senior Scientist Candice Hansen is also a co-author on the paper.
Using data collected by Cassini’s ultraviolet imaging spectrograph (UVIS), the research team headed by lead author of the paper, Don Shemansky, a Cassini UVIS team member with Space Environment Technologies, calculated that Europa contributes 40 times less oxygen than previously thought to its surrounding environment.
Europa is seen as a site of potential life because of indications it has an ocean beneath its crust.
The new study also overturns the 20-year-old idea that Europa's atmosphere is mostly made of molecular oxygen (O2). Instead, the new results show that the moon's gaseous envelope is mostly made of single atoms of oxygen. Researchers believed a process called sputtering produced the oxygen. In this process, charged particles slam into water (H2O) ice on Europa's surface like the opening break in a game of billiards, liberating the oxygen to become part of the atmosphere.
The authors suggest a different, more energetic process could be at work to produce free-flying atoms of oxygen. In this version, ions – which are atoms with an electric charge – are supercharged by Jupiter's fast-rotating magnetosphere. When these ions strike the surface of Europa, they zap molecules of water ice with a big electric jolt, breaking the bonds that hold molecules together.
“These new results really highlight just how interesting and mysterious Europa is. Its youthful surface shows signs of recent – or even current – activity, though firm detection of this activity remains pretty elusive,” Hendrix said.
Visit for a recently released image of Europa.
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