Suprathermal Ion Observations in the Solar Wind and Magnetosheath around the T96 Cassini Encounter with Titan

Abstract:

Cassini had its 96th close flyby of Titan on Dec. 1, 2013. This was the first flyby that found Titan situated outside Saturn’s bowshock in the solar wind. During a several hour period in the solar wind leading up to closest approach, beginning when Cassini was about 22 R_T from Titan, the Cassini/CHEMS sensor, covering the energy per charge range 3-220 keV/e, detected three species of pickup ions: H⁺, H₂⁺, and a species near m/q = 16 (possibly O⁺). All three species had cutoff energies of about 4.3 keV/nuc, implying a solar wind speed of about 450 km/s. The solar wind slowed upon approach to Titan, presumably as it was loaded with ions of Titan origin. T97 occurred about a month later on Jan. 1, 2014, with Titan located in the magnetosheath. However, Cassini did enter the solar wind for a 12 hour period beginning on Dec. 30, 2013, at a distance of about 325 R_T from Titan. During that period CHEMS observed a weak H⁺ pickup ion signal but no H₂⁺or heavier pickup ions, indicating that high intensities of those species are confined to a somewhat limited region near Titan. We will discuss these observations and multiple ion acceleration events (>100 keV) that occurred during the several day period around T96 during which Cassini crossed Saturn’s bowshock 16 times.

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