Other
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufm.p22b..07b&link_type=abstract
American Geophysical Union, Fall Meeting 2006, abstract #P22B-07
Other
5210 Planetary Atmospheres, Clouds, And Hazes (0343), 5405 Atmospheres (0343, 1060), 5475 Tectonics (8149), 6280 Saturnian Satellites, 7853 Spacecraft/Atmosphere Interactions
Scientific paper
The discovery of a water plume at Enceladus' south pole is one of the great unexpected discoveries of the Cassini mission. Joint observations by Cassini's experiments, many of which occurred during a close flyby of the satellite in July 2005, have confirmed the existence of a plume which sends water gas and ice grains into orbit around Saturn. This is the primary source of neutrals in the inner magnetosphere, although other processes are responsible for producing the extended clouds formed from these neutrals (Johnson et al 2006). Ionization of the water product clouds provides the primary source of magnetospheric ions. Observations by the Ultraviolet Spectrometer (UVIS) of star being occulted by the plume imply a source rate of ~300 kg/s of water from the south pole of Enceladus (Hansen et al 2006, Burger et al 2006). No water was detected by UVIS at higher latitudes, although the Ion and Neutral Mass Spectrometer (INMS) did detect water during the inbound and outbound portions of Cassini's flyby trajectory when Cassini northward across the orbital plane (Waite et al 2006). Burger et al (2006) have shown that the INMS observations are consistent with a distributed, possibly global, source of water with a source rate ~2 kg/s which contributes to the water exosphere observed over the outbound (northern) portion of the trajectory. The maximum density measured by INMS, which was coincident with the closest approach of the spacecraft to the south pole, implies a source rate significantly lower than that determined from the UVIS observations. We present models for the Enceladus gas plume consistent with the high density UVIS measurements and the lower density, in situ INMS observations. We assume that water molecules are on ballistic trajectories once they are ejected from the surface and determine the vent geometries, distributed surface distributions, and initial velocity distributions consistent with the spacecraft measurements. Possible observations to discriminate between plume models and implications for future Enceladus flybys are discussed. References: Burger, M.H. et al., in prep, 2006. Hansen, C.J., et al., Science, 311, 1422, 2006. Johnson, R.E., et al., ApJ, 644, L137, 2006. Waite, J.H. et al, Science, 311, 1419, 2006.
Burger Matthew Howard
Johnson Robert E.
Sittler Edward C.
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