Radiation limits on amino acid preservation and chiral measurement at Oxia Planum
Abstract
Amino acid enantiomeric excess (EE) is a potential biosignature, but its measurement requires sufficient surviving material as well as preserved chirality. We derive a criterion that separates abundance-limited from racemization-limited preservation and apply it to the Mars Organic Molecule Analyzer (MOMA) on the ExoMars Rosalind Franklin rover. The model combines cosmic-ray and radiogenic doses with laboratory destruction kinetics and assumed ratios of interconversion to destruction rates. For an initially homochiral population of 1000~ppmw, the surviving EE is 58\% or 25\% when the total abundance reaches 1~ppmw for rate ratios of 0.04 or 0.10, respectively. This abundance criterion does not ensure that both enantiomers can be quantified. Applying provisional estimates of 1~ppmw per enantiomer and 10\% EE, serine at 2~m requires initial concentrations of 340 and 960~ppmw after cosmic-ray exposures of 107 and 108~yr, respectively, under transferred fused-silica--perchlorate kinetics and a 1.57-MGy radiogenic dose. These concentrations exceed measured meteoritic serine abundances, but do not predict the initial Oxia inventory. For organics retained in a closed host since deposition 3.9~Ga ago, the modeled radiogenic dose is 1.6--5.6~MGy across the adopted compositions. In the lower-dose case, drilling to 2~m reduces the total dose by only a factor of 1.5 after 107~yr. The boundaries depend on mineral kinetics and organic residence time; they distinguish preserved chirality from a measurable excess.
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BibTeX
@misc{atri2026radiation,
title = {{Radiation limits on amino acid preservation and chiral measurement at Oxia Planum}},
author = {Dimitra Atri},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.17931},
eprint = {2610.17931},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.17931},
}
RIS
TY - UNPB
TI - Radiation limits on amino acid preservation and chiral measurement at Oxia Planum
AU - Dimitra Atri
PY - 2026
DA - 2026/10/13
PB - arXiv
DO - 10.48550/arxiv.2610.17931
UR - https://arxiv.org/abs/2610.17931
AB - Amino acid enantiomeric excess (EE) is a potential biosignature, but its measurement requires sufficient surviving material as well as preserved chirality. We derive a criterion that separates abundance-limited from racemization-limited preservation and apply it to the Mars Organic Molecule Analyzer (MOMA) on the ExoMars Rosalind Franklin rover. The model combines cosmic-ray and radiogenic doses with laboratory destruction kinetics and assumed ratios of interconversion to destruction rates. For an initially homochiral population of 1000~ppmw, the surviving EE is 58\% or 25\% when the total abundance reaches 1~ppmw for rate ratios of 0.04 or 0.10, respectively. This abundance criterion does not ensure that both enantiomers can be quantified. Applying provisional estimates of 1~ppmw per enantiomer and 10\% EE, serine at 2~m requires initial concentrations of 340 and 960~ppmw after cosmic-ray exposures of 10^7 and 10^8~yr, respectively, under transferred fused-silica--perchlorate kinetics and a 1.57-MGy radiogenic dose. These concentrations exceed measured meteoritic serine abundances, but do not predict the initial Oxia inventory. For organics retained in a closed host since deposition 3.9~Ga ago, the modeled radiogenic dose is 1.6--5.6~MGy across the adopted compositions. In the lower-dose case, drilling to 2~m reduces the total dose by only a factor of 1.5 after 10^7~yr. The boundaries depend on mineral kinetics and organic residence time; they distinguish preserved chirality from a measurable excess.
ER -