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地球与行星物理

ISSN  2096-3955

CN  10-1502/P

Citation: Fa-Yu Jiang, Jun Cui, Ji-Yao Xu, Yong Wei, 2019: Species-dependent ion escape on Titan, Earth and Planetary Physics, 3, 183-189. doi: 10.26464/epp2019020

2019, 3(3): 183-189. doi: 10.26464/epp2019020

PLANETARY SCIENCES

Species-dependent ion escape on Titan

1. 

State Key Laboratory of Space Weather, National Space Science Center, Chinese Academy of Sciences, Beijing 100190, China

2. 

Key Laboratory of Lunar and Deep Space Exploration, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100101, China

3. 

School of Atmospheric Sciences, Sun Yat-sen University, Zhuhai, Guangdong 519082, China

4. 

Chinese Academy of Sciences Center for Excellence in Comparative Planetology, Hefei 230026, China

5. 

Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China

Corresponding author: Jun Cui, cuijun7@mail.sysu.edu.cn

Received Date: 2018-12-05
Web Publishing Date: 2019-05-01

Cassini observations over the past ten years have revealed that Titan possesses a chemically complex ionosphere. In this study, we investigate the relative contributions of different ion species to the total ion escape on Titan, by dividing all ion species probed by the Cassini Ion Neutral Mass Spectrometer (INMS) into six groups according to their mass-to-charge ratios (M/Z). For the three lightest ion groups, with characteristic M/Z of 22, 41, and 52 daltons , the observed scale heights tend to be lower than the scale heights predicted by assuming diffusive equilibrium; for the three heavier groups, observed and predicted scale heights are in general agreement, implying that most ion escape from Titan is by relatively light species, with M/Z < 60 daltons. A diffusion model is constructed to describe the density distribution of each ion group in regions where the effect of ionospheric chemistry could be neglected. The data model comparison predicts an optimal total ion escape rate of 3.1×1024 s–1, of which more than 99% is contributed by relatively light ions with M/Z < 32 daltons.

Key words: Titan; planetary ionospheres; atmospheric escape

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Species-dependent ion escape on Titan

Fa-Yu Jiang, Jun Cui, Ji-Yao Xu, Yong Wei