Titan's Thermospheric Response to Various Plasma Environments

Details Titan's Thermospheric Response to Various Plasma Environments Titan's Thermospheric Response to Various Plasma Environments

Dec 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsm13d..08w&link_type=abstract

American Geophysical Union, Fall Meeting 2010, abstract #SM13D-08

Physics

[2732] Magnetospheric Physics / Magnetosphere Interactions With Satellites And Rings, [5405] Planetary Sciences: Solid Surface Planets / Atmospheres, [6280] Planetary Sciences: Solar System Objects / Saturnian Satellites, [6281] Planetary Sciences: Solar System Objects / Titan

Scientific paper

The Cassini-Huygens mission has been observing Titan since October of 2004 resulting in over 70 targeted flybys. Titan's thermosphere is sampled by the Ion and Neutral Mass Spectrometer (INMS) during several of these flybys. The measured upper atmospheric mass density varies significantly from flyby to flyby. In order to quantify this variability, we calculate the mean atmospheric scale height for a variety of plasma conditions and geospatial parameters and, from these, we infer an effective temperature. In particular, we investigate how these calculated scale heights and temperatures correlate with: (1) the local plasma environment and (2) the type of plasma interaction region sampled during the flyby (i.e. ram, wake, Saturn-facing flank, or anti-Saturn facing flank). Measured mass densities and the inferred temperatures are found to be reduced when INMS samples Titan in Saturn's night side magnetosphere (Saturn local time 9 pm to 3 am), while they are enhanced when INMS samples Titan in the day side magnetosphere (Saturn Local Time between 9 am to 3 pm). Moreover, variations in the upstream plasma environment result in effective temperatures that range from 152.0 ± 1.2 K for plasma sheet type interactions down to 124.4 ± 1.9 K for lobe type interactions (cf. Rymer et al. [2009]; Simon et al. [2010]). Additionally, a flyby's specific Titan-plasma interaction regime (i.e. ram, wake, or flank) significantly influences the inferred temperatures. The wake, ram, and Saturn-facing components exhibit higher overall temperatures than the anti-Saturn-facing region. Finally the data analysis is supplemented with Navier-Stokes model calculations using the Titan Global Ionosphere Thermosphere Model (T-GITM) [Bell et al., 2010]. Our analysis indicates that, during the solar minimum conditions prevailing during the Cassini tour, the plasma interaction plays a significant role in determining the thermal structure of the upper atmosphere and, in certain regions and situations on Titan, may over-ride the expected solar-driven diurnal variation in temperatures.

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