The upper atmosphere of Titan is highly variable as characterized by the variations of the thermospheric and exospheric temperatures from in situ measurements by Cassini at different Titan encounters. A related question has to do with the escape flux of CH4 that might also change with the complex plasma environment and ionospheric conditions. In this study, the atmospheric density profiles obtained by the INMS experiment on Cassini are examined in the context of a bi-Maxwellian approximation proposed by Jiang et al. The results are compared to the escape fluxes generated by magnetospheric and pickup ion sputtering and ionospheric processes. It is found that a CH4 flux at a level of the order of 1023-1025 CH4 s-1 could be maintained during the quiet condition. But episodic events with the corresponding CH4 escape rate reaching as large as 1027 s-1 might be possible. Such a time variability could be indicative of a global change of Titan's atmospheric temperature at relatively short timescales.
|出版狀態||已出版 - 10 6月 2019|