The Structure of Titan's N-2 and CH4 Coronae

doi:10.3847/1538-3881/aa9936

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	The Structure of Titan's N-2 and CH4 Coronae
	Jiang, Fayu 1,2; Cui, Jun 2,3,4; Xu, Jiyao 1
刊名	ASTRONOMICAL JOURNAL
	2017-12-01
卷号	154 期号:6 页码:13
关键词	planets and satellites: atmospheres planets and satellites: individual (Titan)
ISSN号	0004-6256
DOI	10.3847/1538-3881/aa9936
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.
资助项目	National Science Foundation of China (NSFC)[41374178] ; National Science Foundation of China (NSFC)[41525015] ; National Science Foundation of China (NSFC)[41774186] ; Science and Technology Development Fund of Macau SAR (FDCT)[039/2013/A2] ; Science and Technology Development Fund of Macau SAR (FDCT)[082/2015/A3]
WOS关键词	HOT OXYGEN CORONA ; LYMAN-ALPHA-DATA ; UPPER-ATMOSPHERE ; THERMAL STRUCTURE ; HYDROGEN ; VENUS ; ESCAPE ; MARS ; THERMOSPHERE ; EXOSPHERE
WOS研究方向	Astronomy & Astrophysics
语种	英语
出版者	IOP PUBLISHING LTD
WOS记录号	WOS:000425446600001
资助机构	National Science Foundation of China (NSFC) ; National Science Foundation of China (NSFC) ; Science and Technology Development Fund of Macau SAR (FDCT) ; Science and Technology Development Fund of Macau SAR (FDCT) ; National Science Foundation of China (NSFC) ; National Science Foundation of China (NSFC) ; Science and Technology Development Fund of Macau SAR (FDCT) ; Science and Technology Development Fund of Macau SAR (FDCT) ; National Science Foundation of China (NSFC) ; National Science Foundation of China (NSFC) ; Science and Technology Development Fund of Macau SAR (FDCT) ; Science and Technology Development Fund of Macau SAR (FDCT) ; National Science Foundation of China (NSFC) ; National Science Foundation of China (NSFC) ; Science and Technology Development Fund of Macau SAR (FDCT) ; Science and Technology Development Fund of Macau SAR (FDCT)
内容类型	期刊论文
源URL	[http://ir.bao.ac.cn/handle/114a11/37191]
专题	中国科学院国家天文台
通讯作者	Jiang, Fayu
作者单位	1.Chinese Acad Sci, Natl Space Sci Ctr, State Key Lab Space Weather, Beijing, Peoples R China 2.Chinese Acad Sci, Natl Astron Observ, Key Lab Lunar & Deep Space Explorat, Beijing, Peoples R China 3.Sun Yat Sen Univ, Sch Atmospher Sci, Zhuhai, Peoples R China 4.Macau Univ Sci & Technol, Lunar & Planetary Sci Lab, Space Sci Inst, Macau, Peoples R China
推荐引用方式 GB/T 7714	Jiang, Fayu,Cui, Jun,Xu, Jiyao. The Structure of Titan's N-2 and CH4 Coronae[J]. ASTRONOMICAL JOURNAL,2017,154(6):13.
APA	Jiang, Fayu,Cui, Jun,&Xu, Jiyao.(2017).The Structure of Titan's N-2 and CH4 Coronae.ASTRONOMICAL JOURNAL,154(6),13.
MLA	Jiang, Fayu,et al."The Structure of Titan's N-2 and CH4 Coronae".ASTRONOMICAL JOURNAL 154.6(2017):13.