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.
Waite
J Hunter
JH
Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan, Ann Arbor, MI 48109, USA.
Combi
Michael R
MR
Ip
Wing-Huen
WH
Cravens
Thomas E
TE
McNutt
Ralph L
RL
Kasprzak
Wayne
W
Yelle
Roger
R
Luhmann
Janet
J
Niemann
Hasso
H
Gell
David
D
Magee
Brian
B
Fletcher
Greg
G
Lunine
Jonathan
J
Tseng
Wei-Ling
WL
D000641:Ammonia / Q000032:analysis; D001272:Atmosphere; D002245:Carbon Dioxide / Q000032:analysis; D019419:Evolution, Planetary; D005118:Extraterrestrial Environment / Q000737:chemistry; D013058:Mass Spectrometry; D008697:Methane / Q000032:analysis; D018539:Saturn; D018531:Spacecraft; D014867:Water / Q000032:analysis
D014867:Water; D002245:Carbon Dioxide; D000641:Ammonia; D008697:Methane