期刊
ASTROPHYSICAL JOURNAL
卷 770, 期 2, 页码 -出版社
IOP PUBLISHING LTD
DOI: 10.1088/0004-637X/770/2/132
关键词
molecular processes; planets and satellites: atmospheres; planets and satellites: composition; planets and satellites: individual (Titan); radiation mechanisms: non-thermal
资金
- Italian Space Agency [ASI I/015/09]
- Spanish MINECO [AYA2011-23552]
- CONSOLIDER program [CSD2009-00038]
- EC FEDER funds
- MINECO under its Ramon y Cajal subprogram
- NASA Postdoctoral Program at the Ames Research Center
- NASA
In this paper, we analyze the strong unidentified emission near 3.28 mu m in Titan's upper daytime atmosphere recently discovered by Dinelli et al. We have studied it by using the NASA Ames PAH IR Spectroscopic Database. The polycyclic aromatic hydrocarbons (PAHs), after absorbing UV solar radiation, are able to emit strongly near 3.3 mu m. By using current models for the redistribution of the absorbed UV energy, we have explained the observed spectral feature and have derived the vertical distribution of PAH abundances in Titan's upper atmosphere. PAHs have been found to be present in large concentrations, about (2-3) x 10(4) particles cm(-3). The identified PAHs have 9-96 carbons, with a concentration-weighted average of 34 carbons. The mean mass is similar to 430 u; the mean area is about 0.53 nm(2); they are formed by 10-11 rings on average, and about one-third of them contain nitrogen atoms. Recently, benzene together with light aromatic species as well as small concentrations of heavy positive and negative ions have been detected in Titan's upper atmosphere. We suggest that the large concentrations of PAHs found here are the neutral counterpart of those positive and negative ions, which hence supports the theory that the origin of Titan main haze layer is located in the upper atmosphere.
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