Abstract EANA2026-29

The search for life beyond Earth relies on identifying environments capable of generating, hosting, and preserving molecular biosignatures. Terrestrial analogs are essential for this effort because they reproduce mineralogical and physicochemical conditions relevant to Mars and the ocean worlds. Among these, hydrothermal systems and saline lakes offer complementary insights: hot springs provide high‑temperature, silica‑ and sulfate‑rich niches analogous to ancient Martian hydrothermal settings, whereas evaporitic lakes model brine‑mediated preservation processes pertinent to Noachian paleolakes and to the subsurface oceans of icy moons. Both environments are central to astrobiology, with hydrothermal systems widely regarded as plausible cradles for the emergence of life on early Earth, and evaporitic basins representing the last potentially habitable niches on Mars.

To investigate how biosignatures vary across these contrasting environments, we analyzed two high‑altitude analogs in the Indian Himalayas (Ladakh region): the neutral‑waters Puga hot springs and the alkaline brine lake Tso Kar. Mineralogical and bulk geochemical data revealed distinct physicochemical gradients at each site, delineating potential ecological niches and preservation windows. Molecular and compound‑specific isotopic analyses of lipid biomarkers further resolved the biological imprints associated with these settings. Puga exhibited lipid assemblages and δ¹³C patterns dominated by prokaryotic sources—including cyanobacteria, Chloroflexi, and sulfate‑reducing bacteria—together with isotopic signatures consistent with Calvin and 3‑hydroxypropionate pathways. In contrast, Tso Kar displayed a more pronounced eukaryotic signal, characterized by sterols and polyunsaturated fatty acids, and δ¹³C values indicative of alternative autotrophic metabolisms other than the Calvin cycle, such as the reductive tricarboxylic acid cycle.

To contextualize these findings, we integrated them into a global dataset of hydrothermal and evaporitic analogs worldwide. This comparison revealed a marked environmental control over lipid biosignatures, providing a basis for prioritizing exploration targets. Evaporitic lakes worldwide share a broader suite of lipid compounds (n = 25), yet many are source‑unspecific and may arise abiotically, particularly saturated n‑alkanes and n‑alkanoic acids. In contrast, hot spring systems consistently host a smaller but more diagnostic set of lipids (n = 14), unambiguously biogenic and characteristically linked to bacteria such as unsaturated and iso/anteiso alkanoic acids. These patterns highlight the superior diagnostic potential of hydrothermal environments for life‑detection efforts, while underscoring the importance of evaporitic systems for understanding long‑term organic preservation in brines relevant to ocean worlds.

Together, these results expand the inventory of biosignatures from underexplored Himalayan analogs and reinforce the value of lipids—the most resistant and preservation‑prone class of molecular biosignatures—for planetary exploration. By linking mineralogical context, organic geochemistry, molecular distributions, and isotopic pathways, this study provides a framework for identifying the biosignatures most likely to persist in hydrothermal and evaporitic environments on Mars, Europa, and Enceladus. This integrative approach offers a strategic foundation for prioritizing sampling targets and analytical strategies in future life‑detection missions to Mars and the ocean worlds.

 

Funding: This work was funded by the Spanish Ministry of Science and Innovation/State Agency of Research MCIN/AEI/10.13039/501100011033 and by “ERDF A way of making Europe” through the projects RYC2018-023943-I, PID2021-126746NBI00, and CNS2024-154541 (L.S.G.); and PID2022-140180B-C21 (D.C.).