Cassini ion and neutral mass spectrometer: Enceladus plume composition and structure.


The Cassini spacecraft passed within 168.2 kilometers of the surface above the southern hemisphere at 19:55:22 universal time coordinated on 14 July 2005 during its closest approach to Enceladus. Before and after this time, a substantial atmospheric plume and coma were observed, detectable in the Ion and Neutral Mass Spectrometer (INMS) data set out to a distance of over 4000 kilometers from Enceladus. INMS data indicate that the atmospheric plume and coma are dominated by water, with significant amounts of carbon dioxide, an unidentified species with a mass-to-charge ratio of 28 daltons (either carbon monoxide or molecular nitrogen), and methane. Trace quantities (<1%) of acetylene and propane also appear to be present. Ammonia is present at a level that does not exceed 0.5%. The radial and angular distributions of the gas density near the closest approach, as well as other independent evidence, suggest a significant contribution to the plume from a source centered near the south polar cap, as distinct from a separately measured more uniform and possibly global source observed on the outbound leg of the flyby.


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@article{Waite2006CassiniIA, title={Cassini ion and neutral mass spectrometer: Enceladus plume composition and structure.}, author={J Hunter Waite and Michael R. Combi and Wing-Huen Ip and Thomas E. Cravens and Ralph L. McNutt and Wayne T Kasprzak and R Yelle and Janet G. Luhmann and Hasso B. Niemann and David A. Gell and Brian A Magee and Greg Fletcher and Jonathan I. Lunine and Wei-Ling Tseng}, journal={Science}, year={2006}, volume={311 5766}, pages={1419-22} }