Cassini sheds new light on Europa's atmosphere

Astronomers have revealed that analysis of NASA's Cassini spacecraft's data collected during its 2001 flyby of Jupiter sheds new light on the atmosphere of the planet's moon Europa.

According to the researchers, the recently discovered gas plumes on Europa do not contribute to the thin atmosphere.

PSI Senior Scientist Amanda Hendrix said that 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.

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.

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.

The study was published in The Astrophysical Journal.