2021年5月1日
Stability of Atmospheric Redox States of Early Mars Inferred from Time Response of the Regulation of H and O Losses
The Astrophysical Journal
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- 巻
- 912
- 号
- 2
- 開始ページ
- 135
- 終了ページ
- 135
- 記述言語
- 英語
- 掲載種別
- 研究論文(学術雑誌)
- DOI
- 10.3847/1538-4357/abf0ac
- 出版者・発行元
- American Astronomical Society
The ratio of total losses of H and O from the atmosphere is crucial for determining the Martian atmospheric redox state. The H and O escapes are shown to be regulated in a stoichiometric 2:1 ratio in a converged model of present-day Mars over a timescale of ∼105 yr, which is called self-regulation. Self-regulation timescales under different atmospheric conditions on early Mars are not well understood. Here we use a 1D photochemical model to calculate the timescales of self-regulation for denser CO2 atmospheres with various surface temperatures as benchmark cases for early Mars. Self-regulation is driven by variations in the amount of O2 or CO in the atmosphere, depending on the atmospheric redox state. Self-regulation timescales are likely to be controlled by the net redox balance. A 1 bar CO2 atmosphere with a surface temperature of 240 K has a self-regulation timescale of a few million years. Denser atmospheres of early Mars have a longer regulation timescale and are less redox-stable than the atmosphere of present-day Mars. Obliquity variations cause atmospheric CO2 fluctuations, producing a difference in the self-regulation timescale between high and low obliquity. Because an increase in CO2 suppresses H escape, the net effect of the obliquity cycle could have driven the atmospheric redox states to be more reducing. Our results also suggest the possibility of a CO-dominated atmosphere of 10-100 mbars at 3 Ga. The redox state of ancient Mars might have fluctuated more easily than that of the present.
- リンク情報
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- DOI
- https://doi.org/10.3847/1538-4357/abf0ac
- URL
- https://iopscience.iop.org/article/10.3847/1538-4357/abf0ac
- URL
- https://iopscience.iop.org/article/10.3847/1538-4357/abf0ac/pdf
- Scopus
- https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85106345722&origin=inward
- Scopus Citedby
- https://www.scopus.com/inward/citedby.uri?partnerID=HzOxMe3b&scp=85106345722&origin=inward
- ID情報
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- DOI : 10.3847/1538-4357/abf0ac
- ISSN : 0004-637X
- eISSN : 1538-4357
- SCOPUS ID : 85106345722