Long Term Time Variations of the Suprathermal Ion Composition in Saturn's Magnetosphere

Details Long Term Time Variations of the Suprathermal Ion Composition in Saturn's Magnetosphere Long Term Time Variations of the Suprathermal Ion Composition in Saturn's Magnetosphere

Dec 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsm23a1904d&link_type=abstract

American Geophysical Union, Fall Meeting 2010, abstract #SM23A-1904

Physics

[2740] Magnetospheric Physics / Magnetospheric Configuration And Dynamics, [2756] Magnetospheric Physics / Planetary Magnetospheres, [6275] Planetary Sciences: Solar System Objects / Saturn

Scientific paper

Studying the time variations of the ion composition in Saturn’s magnetosphere provides insight into the variability of the different plasma sources (Enceladus, Titan, Saturn, the solar wind, etc.). Here we study long term variations from late 2004 to mid 2010 utilizing data from four separate time periods: 2004 348-2005 106, 2005 265-2006 182, 2007 177-2007 338, and 2009 285-2010 207. These are periods during which Cassini had nearly equatorial orbits; they vary in length from 124 to 287 days. Using data from the Charge-Energy-Mass Spectrometer (CHEMS) on Cassini, we determine the average composition of suprathermal (E/Q=27-220 keV/e) ions in Saturn’s equatorial ring current (L=7-16, |Z| < 1 RS) for each period. The species examined are W+ (O++OH++H2O++ H3O+), H+, H2+, the three species that dominate the number density, and also He++, He+, and O++. These species are tracers of the various plasma sources: W+ and O++ from Enceladus, H2+ from Titan, He++ and He+ from the solar wind, and H+ (mixed Saturn, Enceladus, and solar wind). We find that the total number density varies by less than a factor of two over the six years. Some of this variation is due to the different local times sampled during the four periods. H+ and W+ comprise more than 90% of the total number density and their fractional abundance vary by less than 20%. The fractional abundance of H2+, the third most abundant species, ranges from 0.04-0.07. The fractional abundance of the solar wind species vary by more than a factor of 4. Above 83 keV/e we can also measure the molecular species O2+, which appears to show a factor of 7 decline in fractional abundance from early to late in the mission.

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