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Alteration of the Carbon and Nitrogen Isotopic Composition in the Martian Surface Rocks Due to Cosmic Ray ExposureC-13/C-12 and N-15/N-14 isotopic ratios are pivotal for our understanding of the Martian carbon cycle, history of the Martian atmospheric escape, and origin of the organic compounds on Mars. Here we demonstrate that the carbon and nitrogen isotopic composition of the surface rocks on Mars can be significantly altered by the continuous exposure of Martian surface to cosmic rays. Cosmic rays can effectively produce C-13 and N-15 isotopes via spallation nuclear reactions on oxygen atoms in various Martian rocks. We calculate that in the top meter of the Martian rocks, the rates of production of both C-13 and N-15 due to galactic cosmic rays (GCRs) exposure can vary within 1.5-6 atoms/cm3/s depending on rocks' depth and chemical composition. We also find that the average solar cosmic rays can produce carbon and nitrogen isotopes at a rate comparable to GCRs in the top 5-10 cm of the Martian rocks. We demonstrate that if the total carbon content in a surface Martian rock is <10 ppm, then the "light," potentially "biological" C-13/C-12 ratio would be effectively erased by cosmic rays over 3.5 billion years of exposure. We found that for the rocks with relatively short exposure ages (e.g., 100 million years), cosmogenic changes in N-15/N-14 ratio are still very significant. We also show that a short exposure to cosmic rays of Allan Hills 84001 while on Mars can explain its high-temperature heavy nitrogen isotopic composition (N-15/N-14). Applications to Martian meteorites and the current Mars Science Laboratory mission are discussed.
Document ID
Document Type
Reprint (Version printed in journal)
External Source(s)
Pavlov, A. A. (NASA Goddard Space Flight Center Greenbelt, MD United States)
Pavlov, A. K. (Academy of Sciences (Russia) Saint Petersburg, Russian Federation)
Ostryakov, V. M. (Saint Petersburg State Polytechnical Univ. Saint Petersburg, Russian Federation)
Vasilyev, G. I. (Academy of Sciences (Russia) Saint Petersburg, Russian Federation)
Mahaffy, P. (NASA Goddard Space Flight Center Greenbelt, MD United States)
Steele, A. (Carnegie Institution of Washington Washington, DC, United States)
Date Acquired
May 3, 2016
Publication Date
June 26, 2014
Publication Information
Publication: Journal of Geophysical Research-Planets
Volume: 119
Issue: 6
ISSN: 2169-9097
Subject Category
Lunar and Planetary Science and Exploration
Report/Patent Number
Distribution Limits
cosmic ray exposure
isotopic composition
carbon and nitrogen