Abstract EANA2026-94

A common definition of life is a self-sustaining chemical system capable of Darwinian evolution. The former requires life to regulate how, when, and where molecules interact and reactions take place. Reactions are principally determined by the frontier orbitals, the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO). Frontier-orbital derived biosignatures (FOBs) represent a new class of molecular biosignatures that can be immediately deployed on current and future space missions, including ExoMars. One example is the amino acid abundance-weighted variance of the HOMO-LUMO gap (AA wvar HLG), which achieves >95% accuracy in class separation between 189 samples derived from biotic (N=87) and abiotic (N=102) environments. Machine learning using all 11 molecular properties x 3 metrics (33 features) tested did not significantly improve the results, highlighting the overwhelming informative nature of the HLG. Using this result, we developed LUMOS (Life Unveiled via Molecular Orbital Signatures) to provide a Bayesian statistical framework that estimates confidence in biogenicity. Monte Carlo analyses show that LUMOS is robust even with low (0.01) prior beliefs in biogenicity. LUMOS is mechanistic, sensitive, specific, robust, and mission ready. It can be applied to any instrument able to quantify amino acid abundances, such as the ExoMars Mars Organic Molecule Analyzer (MOMA). The ExoMars Rosalind Franklin Rover is the first Mars vehicle capable of drilling to 2 m. Modelling survival of molecular biosignatures using a last universal common ancestor (LUCA)-like microbial cell composition as a baseline suggests a strategy for life detection. At typical 100 My exposure ages, DNA (if present) would represent a better target than amino acids at depths < 1.25 m, although amino acids may be detectable at a lower initial cell density at deposition at greater depths. At an exposure age of 10 My, amino acids would be expected to dominate at all depths compared to DNA. Sampling such a low exposure age may be possible by targeting ejecta from the Mojave impact event (~10.1 My). Notably, thousands of confirmed Mojave-derived secondary impact craters exist in Oxia Planum. If MOMA successfully detects and quantifies the abundance of amino acids on Mars, LUMOS can be directly applied, complementing other analyses (e.g., amino acid chirality). We note that LUMOS does not depend upon any specific set of amino acids, only the ability to quantify amino acids and thereby associate their abundance with a molecular property of interest (e.g., the HLG). Therefore, if life on Mars existed and utilized amino acids, we believe LUMOS would provide a direct and robust measure. The preservation of low-HLG amino acids over geologic time is not yet well characterized, and thus the molecular taphonomy of frontier orbital-derived biosignatures like the wvar HLG remains to be established, making the biggest risk a false-negative. Testing on Earth fossils could help to further assess this risk. Further study is needed to evaluate and extend FOBs to other classes of molecules.