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题名: The Structure of Titan's N-2 and CH4 Coronae
作者: Jiang, Fayu; Cui, Jun; Xu, Jiyao
作者部门: 空间科学部
通讯作者: Jiang, FY (reprint author), Chinese Acad Sci, Natl Space Sci Ctr, State Key Lab Space Weather, Beijing, Peoples R China. ; Jiang, FY (reprint author), Chinese Acad Sci, Natl Astron Observ, Key Lab Lunar & Deep Space Explorat, Beijing, Peoples R China.
关键词: planets and satellites: atmospheres ; planets and satellites: individual (Titan)
刊名: ASTRONOMICAL JOURNAL
ISSN号: 0004-6256
出版日期: 2017
卷号: 154, 期号:6, 页码:271
收录类别: SCI
项目资助者: National Science Foundation of China (NSFC) [41374178, 41525015, 41774186] ; Science and Technology Development Fund of Macau SAR (FDCT) [039/2013/A2, 082/2015/A3]
英文摘要: In this study, we analyze the structures of Titan's N-2 and CH4 coronae using a large data set acquired by the Ion Neutral Mass Spectrometer (INMS) instrument on board Cassini. The N-2 and CH4 densities measured from the exobase up to 2000 km imply a mean exobase temperature of 146 K and 143 K, respectively, which is lower than the mean upper atmospheric temperature by 4 and 7 K. This indicates that on average, Titan possesses a subthermal rather than suprathermal corona. A careful examination reveals that the variability in corona structure is not very likely to be solar driven. Within the framework of the collisionless kinetic model, we investigate how the CH4 energy distribution near the exobase could be constrained if strong CH4 escape occurs on Titan. Several functional forms for the CH4 energy distribution are attempted, assuming two representative CH4 escape rates of 1.2 x 10(25) s(-1) and 2.2 x 10(27) s(-1). We find that the double Maxwellian and power-law distributions can reproduce the shape of the CH4 corona structure as well as the imposed CH4 escape rate. In both cases, the escape rate is contributed by a suprathermal CH4 population on the high-energy tail, with a number fraction below 5% and a characteristic energy of 0.1-0.6 eV per suprathermal CH4 molecule. The coexistence of the subthermal CH4 corona revealed by the INMS data and substantial CH4 escape suggested by some previous works could be reconciled by a significant departure in the exobase CH4 energy distribution from ideal Maxwellian that enhances escape and causes a noticeable redistribution of the corona structure.
语种: 英语
内容类型: 期刊论文
URI标识: http://ir.nssc.ac.cn/handle/122/6210
Appears in Collections:空间科学部_期刊论文

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