Initial interpretation of Titan plasma interaction as observed by the Cassini plasma spectrometer: Comparisons with Voyager 1

Discovery of heavy negative ions in Titan's ionosphere

“…These cool gradually on the inbound trajectory (i.e., on the side away from Saturn), while there is a sharper transition on the outbound side, consistent with ion gyroradius effects associated with pick-up of Titan's atmosphere and ionosphere [e.g., Blanc et al, 2002]. The electric field associated with corotation points away from Saturn, and pickup ions are initially accelerated along this direction in the first part of their cycloidal trajectory; there is related electron cooling here [e.g., Hartle et al, 2006]. Attenuated remnants of this 100 -1000 eV magnetospheric population are seen between 15:18 and 15:40; these play a role in heating the ionosphere and atmosphere [Cravens et al, 2005;Galand et al, 2006] and in ionisation.…”

Negative ion chemistry in Titan's upper atmosphere

“…CAPS and MIMI (Magnetospheric IMaging Instrument) onboard Cassini measured energetic O + ions in Saturn's outer magnetosphere (Hartle et al, 2006;Krimigis et al, 2005). Cravens et al (2008) suggested that, when entering Titan's atmosphere, a few percent of the most energetic ions (27 keV-4 MeV) is converted to negative oxygen ions as a consequence of charge exchange collisions with N 2 .…”

Pickup Particle Acceleration at Comets, Moons and Magnetospheres

“…Recently, pickup ion observations at Titan were re-examined [12,13] and the dominant direction of the early trajectory was confirmed to be along the E direction [13]. In addition, the loss rate due to pickup was found to be ~3.3x10 23 s -1 [13], compared to about an order of magnitude higher rate from the ionosphere [14].…”