期刊
JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS
卷 121, 期 5, 页码 4668-4678出版社
AMER GEOPHYSICAL UNION
DOI: 10.1002/2016JA022349
关键词
ion escape; ambipolar electric field; Mars atmospheric loss; O-2(+) loss at Mars; Mars ionosphere
资金
- NASA through the Mars Exploration Program
- Swedish National Space Board [DNR 162/14]
- Vetenskapsadet [DNR 621-2014-5526]
Recent results from the MAVEN Langmuir Probe and Waves instrument suggest higher than predicted electron temperatures (T-e) in Mars' dayside ionosphere above similar to 180km in altitude. Correspondingly, measurements from Neutral Gas and Ion Mass Spectrometer indicate significant abundances of O-2(+) up to similar to 500km in altitude, suggesting that O-2(+) may be a principal ion loss mechanism of oxygen. In this article, we investigate the effects of the higher T-e (which results from electron heating) and ion heating on ion outflow and loss. Numerical solutions show that plasma processes including ion heating and higher T-e may greatly increase O-2(+) loss at Mars. In particular, enhanced T-e in Mars' ionosphere just above the exobase creates a substantial ambipolar electric field with a potential (e) of several k(B)T(e), which draws ions out of the region allowing for enhanced escape. With active solar wind, electron, and ion heating, direct O-2(+) loss could match or exceed loss via dissociative recombination of O-2(+). These results suggest that direct loss of O-2(+) may have played a significant role in the loss of oxygen at Mars over time.
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