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Nitrogen Fixation at Early Mars

Adams, Danica and Luo, Yangcheng and Wong, Michael L. and Dunn, Patrick and Christensen, Madeline and Dong, Chuanfei and Hu, Renyu and Yung, Yuk (2021) Nitrogen Fixation at Early Mars. Astrobiology, 21 (8). pp. 968-980. ISSN 1531-1074. doi:10.1089/ast.2020.2273.

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The Mars Science Laboratory (MSL) recently discovered nitrates in Gale Crater (e.g., Stern et al., 2015; Sutter et al., 2017). One possible mechanism for ancient nitrate deposition on Mars is through HNOx formation and rain out in the atmosphere, for which lightning-induced NO is likely the fundamental source. This study investigates nitrogen (N₂) fixation in early Mars' atmosphere, with implications for early Mars' habitability. We consider a 1 bar atmosphere of background CO₂, with abundance of N₂, hydrogen, and methane varied from 1% to 10% to explore a swath of potential early Mars climates. We derive lightning-induced thermochemical equilibrium fluxes of NO and HCN by coupling the lightning-rate parametrization from the study of Romps et al. (2014) with chemical equilibrium with applications, and we use a Geant4 simulation platform to estimate the effect of solar energetic particle events. These fluxes are used as input into KINETICS, the Caltech/JPL coupled photochemistry and transport code, which models the chemistry of 50 species linked by 495 reactions to derive rain-out fluxes of HNOx and HCN. We compute equilibrium concentrations of cyanide and nitrate in a putative northern ocean at early Mars, assuming hydrothermal vent circulation and photoreduction act as the dominant loss mechanisms. We find average oceanic concentrations of ∼0.1–2 nM nitrate and ∼0.01–2 mM cyanide. HCN is critical for protein synthesis at concentrations >0.01 M (e.g., Holm and Neubeck, 2009), and our result is astrobiologically significant if secondary local concentration mechanisms occurred. Nitrates may act as high-potential electron acceptors for early metabolisms, although the minimum concentration required is unknown. Our study derives concentrations that will be useful for future laboratory studies to investigate the habitability at early Mars. The aqueous nitrate concentrations correspond to surface nitrate precipitates of ∼1–8 × 10⁻⁴ wt % that may have formed after the evaporation of surface waters, and these values roughly agree with recent MSL measurements.

Item Type:Article
Related URLs:
URLURL TypeDescription
Adams, Danica0000-0001-9897-9680
Dong, Chuanfei0000-0002-8990-094X
Hu, Renyu0000-0003-2215-8485
Yung, Yuk0000-0002-4263-2562
Additional Information:© 2021, Mary Ann Liebert, Inc., publishers. Submitted 7 April 2020; Accepted 26 April 2021. Online Ahead of Print: July 30, 2021. We thank Pin Chen, Armin Kleinboehl, Robin Wordsworth, David Romps, Stuart Bartlett, and Rob Lillis for useful discussions. D.A. was supported by NASA's FINESST program under Proposal Number 80NSSC19K1548. M.L.W. was supported by NASA's Virtual Planetary Laboratory under NASA Astrobiology Institute Cooperative Agreement Number NNA13AA93A and Grant Number 80NSSC18K0829. C.D. was supported by NASA's Habitable Worlds program under Proposal Number 80NSSC18K0288. The research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (80NM0018D0004). This research was initiated under and partially supported by a NASA Habitable Worlds grant (#NNN130466T, later changed to #80NM0018F0612) to Pl R.H. and Co-I Y.L.Y. No competing financial interests exist.
Funding AgencyGrant Number
NASA Earth and Space Science and Technology Fellowship80NSSC19K1548
Subject Keywords:Nitrogen fixation; Early Mars; Astrobiology; Nitrate.
Issue or Number:8
Record Number:CaltechAUTHORS:20210831-224223138
Persistent URL:
Official Citation:Nitrogen Fixation at Early Mars. Danica Adams, Yangcheng Luo, Michael L. Wong, Patrick Dunn, Madeline Christensen, Chuanfei Dong, Renyu Hu, and Yuk Yung. Astrobiology. Aug 2021. 968-980;
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:110680
Deposited By: Tony Diaz
Deposited On:31 Aug 2021 22:53
Last Modified:31 Aug 2021 22:53

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