A tenuous carbon dioxide atmosphere on Jupiter's moon Callisto

An off-limb scan of Callisto was conducted by the Galileo near-infrared map ping spectrometer to search for a carbon dioxide atmosphere. Airglow in the carbon dioxide nu(3) band was observed up to 100 kilometers above the surf ace and indicates the presence of a tenuous carbon dioxide atmosphere with surface pressure of 7.5 x 10(-12) bar and a temperature of about 150 kelvin , close to the surface temperature. A lifetime on the order of 4 years is s uggested, based on photoionization and magnetospheric sweeping. Either the atmosphere is transient and was formed recently or some process is currentl y supplying carbon dioxide to the atmosphere.