After not sensing the atmosphere during an occultation in February, UVIS finally observed the atmosphere first observed by the magnetometer instrument. The UVIS detection came during another stellar occultation, this time of gamma Orionis, or Bellatrix. This star turned out to be a much better one to use than the star used in February, Lambda Sco. During the occultation, UVIS measured the intensity of the star as it passed behind Enceladus and its atmosphere, then reappeared following the occultation. Measurements during ingress (or approaching occultation) indicated a UV absorber between Bellatrix and Cassini over Enceladus south polar region, indicating an atmosphere composed of water vapor. Measurements during egress (or following the occultation) over nightside equatorial regions of Enceladus did not show nearly as strong of a UV absorber. This measurements fits well with the MAG models indicating that the atmosphere is not uniform over the surface of Enceladus and is likely concentrated over the south pole. The lack of a detection during egress could also result from the atmosphere "freezing out" at night.
The presence of water vapor in Enceladus' atmosphere and the lack of atomic oxygen indicates that the atmosphere is produced from the venting or evaporation of water ice from the surface rather than from magnetospheric sputtering, as is the case for the rarefied atmospheres of Europa and Ganymede. Instead the atmosphere has more in common with Io.