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Communication Dans Un Congrès Année : 2018

Nitrogen on Mars: Insights from Curiosity

Résumé

The detection of "fixed" nitrogen on Mars in the form of nitrate by the Sample Analysis at Mars (SAM) instrument suite on the Mars Science Laboratory (MSL) Curiosity Rover [1] has major implications for martian habitability. "Follow the nitrogen" has been proposed as a strategy in the search for both extant and extinct life on Mars [e.g., 2]. Nitrogen is so crucial to life on Earth that life developed metabolic pathways to break the triple bond of N _{}2 and "fix" atmospheric nitrogen to more biologically available molecules for use in proteins and informational polymers. Sequestration of nitrate in regolith has long been predicted to contribute to the removal of N from the martian atmosphere [e.g., 3], and our detections confirm that nitrogen fixation was occurring on ancient Mars. But was this fixed N transformed once deposited, and if so, by what mechanism? An indicator of more complex chemistry would be reduced N, which has, as yet, not been definitively detected on Mars [4]. For example, reduced N in the form of NH _{}3 or NH _{}4 ^{}+ would suggest reduction of nitrate by Fe(II) [5], or even biological fixation or ammonification of atmospheric N. Understanding our detections of nitrogen, particularly within the context of the habitable environment in Yellowknife Bay characterized by the MSL payload, is crucial to assess whether life ever could have existed on ancient Mars.We present 5+ years of analyses and interpretation of nitrate in solid martian drilled and scooped samples by SAM on MSL. Nitrate abundance reported by SAM in situ measurements ranges from non-detection to 681 ± 304 mg/kg [1,6] in the samples examined to date. The measured abundances are consistent with nitrogen fixation via impact generated thermal shock on ancient Mars and/or dry deposition from photochemistry of thermospheric NO. We review the integration of SAM data with terrestrial Mars analog work in order to better understand the timing of nitrogen fixation and mobility of nitrogen on Mars, and thus its availability to putative biology. In particular, the relationship between nitrate and other soluble salts, such as perchlorate, may help reveal the timing of nitrogen fixation and post-depositional behavior of nitrate on Mars [6]. We also discuss potential evidence from SAM data for reduced nitrogen compounds [7]. Finally, we discuss how a comparison of isotopic composition (delta ^{}15N) of nitrate with delta ^{}15N of atmospheric nitrate (delta ^{}15N ∼5 574?, [8]) could to constrain atmospheric loss of N2 and model the evolution of the atmosphere on Mars.
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Dates et versions

insu-04496998 , version 1 (09-03-2024)

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Jennifer Stern, Rafael Navarro-Gonzalez, Christopher P. Mckay, Paul Mahaffy, Brad Sutter, et al.. Nitrogen on Mars: Insights from Curiosity. 42nd COSPAR Scientific Assembly, Jul 2018, Pasadena, United States. pp.Abstract id. F3.3-4-18. ⟨insu-04496998⟩
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