Titan Ion Composition at Magnetosphere-Ionosphere Transition Region

SITTLER, EDWARD C.; HARTLE, R. E.; SHAPPIRIO, M.; SIMPSON, D. J.; COOPER, J. F.; BURGER, M. H.; JOHNSON, R. E.; BERTUCCI, C.; LUHMAN, J. G.; LEDVINA, S. A.; SZEGO, K.; COATES, A. J.; CRARY, F.; YOUNG, D. T.

Congreso; American Astronomical Society, DPS meeting #38; 2006

Using Cassini Plasma Spectrometer (CAPS) Ion Mass Spectrometer (IMS) ion composition data, we will investigate the compositional changes at the transition region between Saturn´s magnetospheric flow and Titan´s upper ionosphere. It is this region where scavenging of Titan´s upper ionosphere can occur, where it is then dragged away by the magnetospheric flow as cold plasma for Saturn´s magnetosphere. This cold plasma may form plumes as originally proposed by (1) during the Voyager 1 epoch. This source of cold plasma may have a unique compositional signature such as methane group ions. Water group ions that are observed in Saturn´s outer magnetosphere (2, 3) are relatively hot and probably come from the inner magnetosphere where they are born from fast neutrals escaping Enceladus (4) and picked up in the outer magnetosphere as hot plasma (5). This scenario will be complicated by pickup methane ions within Titan´s mass loading region, as originally predicted by (6) based on Voyager 1 data and observationally confirmed by (3, 7) using CAPS IMS data. But, CH4+ ions or their fragments can only be produced as pickup ions from Titan´s exosphere which can extend beyond the transition region of concern here, while CH5+ ions can be scavenged from Titan´s ionosphere. We will investigate these possibilities.