Effects of Pickup Ions on Titan's Interaction With Saturn's Magnetosphere During the T9 Flyby

HARTLE, R. E.; SITTLER, E. C.; LIPATOV, A.; BERTUCCI, C.; COATES, A. J.; SZEGO, K.; SHAPPIRIO, M. D.; SIMPSON, D. G.

Congreso; AGU Spring Meeting 2008; 2008

The plasma wake formed by the interaction of Saturn´s rotating magnetosphere with Titan was observed by the Cassini Plasma Spectrometer (CAPS) Electron Spectrometer (ELS) and Ion Mass Spectrometer (IMS) during the T9 flyby (Coates et al., 2007; Szego et al, 2007). Recent analysis of the CAPS ion mass spectrometer measurements by Sittler et al. [2008] has revealed that protons dominate the ion composition of Saturn´s magnetosphere plasma flowing upstream of Titan during the T9 flyby. They show that light magnetospheric ions predominantly extend as far as T9´s trajectory because Titan is sufficiently below Saturn´s neutral sheet (Bertucci, et al., 2007), the region expected to confine the bulk of the heavy ions. Previous interaction studies for other flybys included significant fractions of heavy ions in the magnetosphere such as O+ along with protons. In contrast, the momentum of the magnetospheric plasma interacting with Titan during T9 is significantly lower than considered in previous flyby studies. In this case, the lighter proton magnetosphere plasma interacts noticeably with the lighter pickup ions, H2+ and H+, playing a more important role in mass loading and deflecting magnetosphere plasma around Titan. The influence of these processes extends to great altitudes (and possibly out to the Hill sphere), well beyond the inner region where mass loading by N2+ and CH4+ pickup ions is dominant. This outer region begins beyond an altitude of about a Titan radius, where H2 and H are the dominant exosphere constituents as are their pickup ion progeny. The extent of this much larger sphere of influence on the interaction is analyzed using previously developed pickup ion and mass loading models. Also described are the effects of the heavier pickup ions, N2+ and CH4+, on the interaction closer to Titan. Results from a hybrid model of Lipatov et al. [2008] will also be applied to this study. Coates, A. J., et al., GRL, Vol. 34, L24S05, 2007. Szego, K., et al., GRL, Vol. 34, L24S03, 2007. Sittler, E, C. et al., Spring AGU meeting, 2008. Bertucci, C., et al., GRL, Vol. 34, L24S02, 2007. Lipatov, A., et al. Spring AGU meeting, 2008.