![Radiogenic dose and the benefit of drilling. (a) GCR dose versus depth for constant-depth and steadily exhuming horizons, compared with the depth-independent radiogenic dose. Shading spans the radiogenic dose of the baseline composition at 3 Ga (0.9 MGy) and that of the regional GRS abundances at 3.9 Ga (5.6 MGy). Where a curve crosses the radiogenic level, the two doses are equal. (b) Total-dose reduction at 100–101 and 199–200 cm versus exposure age; dashed lines are the GCR-only shielding factors. Dotted lines mark effective ages for 10 and 100 nm yr−1 exhumation. -- [astro-ph.EP]](https://i0.wp.com/astrobiology.com/wp-content/uploads/2026/10/Radiation.png?fit=1200%2C674&ssl=1)
[astro-ph.EP] 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 1000ppmw, the surviving EE is 58% or 25% when the total abundance reaches 1ppmw 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 1ppmw per enantiomer and 10% EE, serine at 2m requires initial concentrations of 340 and 960ppmw after cosmic-ray exposures of 107 and 108yr, 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 3.9Ga ago, the modeled radiogenic dose is 1.6–5.6MGy across the adopted compositions.
In the lower-dose case, drilling to 2m reduces the total dose by only a factor of 1.5 after 107yr. The boundaries depend on mineral kinetics and organic residence time; they distinguish preserved chirality from a measurable excess.
Dimitra Atri
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM); Space Physics (physics.space-ph)
Cite as: arXiv:2610.17931 [astro-ph.EP] (or arXiv:2610.17931v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2610.17931
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Submission history
From: Dimitra Atri
[v1] Tue, 13 Oct 2026 08:17:16 UTC (164 KB)
https://arxiv.org/abs/2610.17931
Astrobiology,
