The Importance of Aqueous Metabolites in the Martian Subsurface for Understanding Habitability, Organic Chemical Evolution, and Potential Biology
Aqueous metabolites in terrestrial subsurface environments provide critical analog frameworks for assessing the habitability of Martian subsurface ice. On Earth, they play critical roles in sustaining microbial life within soils, permafrost, and groundwater environments and their availability shape microbial community compositions, activity, and adaptability to changes in environmental conditions, enabling communities to persist over millennial timescales. The counterpart to aqueous-soluble organics is the insoluble organic matter pool that makes up the largest portion of organic matter in natural samples and includes most types of organic signatures indicative of biological processes. Employing a range of sample preparation, molecular separation, detection, and imaging techniques enables the characterization of both labile (i.e., soluble and reactive) and recalcitrant (i.e., insoluble, non-reactive; include macromolecules) organic pools. Multiple orthogonal analytical modalities strengthen interpretations of signatures that we associate with biology as we know it and don't know it, by constraining possible abiotic sources, validating measurements across distinct techniques, and ensuring flexibility to interrogate diverse organic chemistries encountered in Martian subsurface environments. This holistic triage approach aligns with the priorities articulated in the Mars Exploration Program Analysis Group's Search for Life -Science Analysis Group (SFL-SAG) Charter for a medium-class Mars mission focused on extant life detection.