Photochemical escape from Mars as constrained by MAVEN in situ measurements and recent modeling
Abstract
Atmospheric loss has been a primary driver of climate evolution over Martian history. One major loss process is photochemical escape, whereby dissociative reactions in the Martian upper ionosphere provide sufficient energy for the atomic products of the reaction to escape Mars' gravity. O, N, C, and H have been escaping from Mars in this manner over Martian history, their escape rates depending on solar extreme ultraviolet irradiance (which was much higher in the past) and the composition of the atmosphere near the exobase. While escaping atoms cannot be directly detected, the MAVEN orbiter measures all the necessary quantities in situ, when combined with appropriate modeling of hot atom transport, allow photochemical escape rates to be calculated. Using this approach, Lillis et al. [2017] reported oxygen escape rates of 1 to 7 x 10$ ^{25}$ s$ ^{-1}$ with a greater-than-linear dependence on solar EUV ionization frequency, implying the loss of 80-300 mbar of oxygen over 4 Ga. However, updated and significantly improved differential hot atom collision cross-sections have now been calculated from first principles [Gacesa et al., 2019]. We will thus present updated estimates of photochemical escape flux using these new cross-sections and ~2 years of new data. In addition, we will present updated estimates of carbon photochemical escape from the recent work of Lo et al. [2020]. We will place these new estimates in the context of evolving understanding of all atmospheric loss processes at Mars and their effects on Martian climate over solar system history.
- Publication:
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43rd COSPAR Scientific Assembly. Held 28 January - 4 February
- Pub Date:
- January 2021
- Bibcode:
- 2021cosp...43E.766L