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The Structure of Titan's N-2 and CH4 Coronae
Jiang, Fayu; Cui, Jun; Xu, Jiyao; 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.
Department空间科学部
Source PublicationASTRONOMICAL JOURNAL
2017
Volume154Issue:6Pages:271
ISSN0004-6256
Language英语
KeywordPlanets And Satellites: Atmospheres Planets And Satellites: Individual (Titan)
AbstractIn 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.
Indexed BySCI
Document Type期刊论文
Identifierhttp://ir.nssc.ac.cn/handle/122/6210
Collection空间科学部
Corresponding AuthorJiang, 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.
Recommended Citation
GB/T 7714
Jiang, Fayu,Cui, Jun,Xu, Jiyao,et al. The Structure of Titan's N-2 and CH4 Coronae[J]. ASTRONOMICAL JOURNAL,2017,154(6):271.
APA Jiang, Fayu,Cui, Jun,Xu, Jiyao,Jiang, FY ,&Jiang, FY .(2017).The Structure of Titan's N-2 and CH4 Coronae.ASTRONOMICAL JOURNAL,154(6),271.
MLA Jiang, Fayu,et al."The Structure of Titan's N-2 and CH4 Coronae".ASTRONOMICAL JOURNAL 154.6(2017):271.
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