Strong Depletion Of 13C in CO Induced By Photolysis Of CO2 In The Martian Atmosphere Calculated By A Photochemical Model

By Keith Cowing
Status Report
February 27, 2023
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Strong Depletion Of 13C in CO Induced By Photolysis Of CO2 In The Martian Atmosphere Calculated By A Photochemical Model
Number density profiles of each chemical species. — astro-ph.EP

The isotopic signature of atmospheric carbon offers a unique tracer for the history of the Martian atmosphere and the origin of organic matter on Mars.

Photolysis of CO2 is known to induce strong isotopic fractionation of carbon between CO2 and CO. However, its effect on the carbon isotopic compositions in the Martian atmosphere remains uncertain. Here we develop a 1-D photochemical model considering isotopic fractionation via photolysis of CO2 to estimate the vertical profiles of the carbon isotopic compositions of CO and CO2 in the Martian atmosphere.

We find that CO is depleted in 13C compared with CO2 at each altitude due to the fractionation via CO2 photolysis: the minimum value of δ13C in CO is about −170 per mil under the standard eddy diffusion setting. This result supports the hypothesis that fractionated atmospheric CO is responsible for the production of the 13C-depleted organic carbon in Martian sediments detected by Curiosity Rover through the conversion of CO into organic materials and their deposition on the surface.

The photolysis and transport-induced fractionation of CO we report here leads to a ∼15 % decrease in the amount of inferred atmospheric loss when combined with the present-day fractionation of the atmosphere and previous studies of carbon escape to space. The fractionated isotopic composition of CO in the Martian atmosphere may be observed by ExoMars Trace Gas Orbiter (TGO) and ground-based telescopes, and escaping ion species produced by the fractionated carbon-bearing species may be detected by Martian Moons eXploration (MMX) in the future.

Tatsuya Yoshida, Shohei Aoki, Yuichiro Ueno, Naoki Terada, Yuki Nakamura, Kimie Shiobara, Nao Yoshida, Hiromu Nakagawa, Shotaro Sakai, Shungo Koyama

Comments: 13 pages, 6 figures
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2302.12457 [astro-ph.EP] (or arXiv:2302.12457v1 [astro-ph.EP] for this version)
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Submission history
From: Tatsuya Yoshida
[v1] Fri, 24 Feb 2023 05:15:12 UTC (978 KB)

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻