Cassini UltraViolet Imaging Spectrograph (UVIS) Observations of Enceladus' Plume

Details Cassini UltraViolet Imaging Spectrograph (UVIS) Observations of Enceladus' Plume Cassini UltraViolet Imaging Spectrograph (UVIS) Observations of Enceladus' Plume

Dec 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufm.p21f..04h&link_type=abstract

American Geophysical Union, Fall Meeting 2005, abstract #P21F-04

Physics

0343 Planetary Atmospheres (5210, 5405, 5704), 6005 Atmospheres (1060), 6280 Saturnian Satellites

Scientific paper

On July 14, 2005, the Cassini UltraViolet Imaging Spectrograph (UVIS) observed the occultation of Bellatrix (gamma Orionis) as it passed behind Enceladus as seen from the spacecraft. The UVIS High Speed Photometer recorded a decrease in signal intensity ~24 seconds prior to occultation of the star by the hard limb, consistent with the presence of an atmosphere. The UVIS Far UltraViolet (FUV) channel recorded absorption features as the starlight passed through the atmosphere. The absorptions allowed us to identify water vapor as the primary composition of the atmosphere, with a column density of ~1.5e16 per square cm. This is the column density at 20 to 40 km above the surface. Non- detection of absorption features associated with CO, H2, and molecular oxygen allows us to place upper limits on the mixing ratio of these gases with respect to water. The quantity of water vapor coming from Enceladus is adequate to supply the atomic oxygen detected in the Saturn system by UVIS and to re-supply Saturn's E ring. An occultation of lambda Scorpius in February of 2005 did not show any sign of an atmosphere, and the presence of an atmosphere was also not sensed during the occultation egress of Bellatrix. This allows us to conclude that the water vapor cloud is localized - the atmosphere of Enceladus is more like a plume and not global in extent.

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