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

Friday, 19 December 2014
Douglas C Hamilton1, David G Wannlund1, Cesar Bertucci2 and Donald G Mitchell3, (1)University of Maryland, College Park, MD, United States, (2)Institute for Astronomy and Space Physics, CONICET/UBA, Buenos Aires, Argentina, (3)Applied Physics Laboratory Johns Hopkins, Laurel, MD, United States
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 RT 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 RT 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.