Abstract EANA2025-141

Since prehistoric times, caves have fulfilled essential roles in human evolution, acting as natural refuges and spaces for artistic expression and cultural practices. Today, these subsurface environments, particularly lava tubes, given the identification of analogous structures on Mars, are emerging as strategic assets in astrobiology and planetary sciences. On Earth, this type of caves, formed during volcanic eruptions by flowing lava, offers thermally stable and chemically sheltered microhabitats capable of hosting microbial ecosystems and preserving biosignatures over geological timescales. On other planets, they may serve similar dual roles: as protective habitats for extant or extinct microbial life and as future refuges for human exploration.
Drawing on a decade of multidisciplinary research in lava tubes worldwide, as well as recent analogue missions, we have explored how terrestrial lava tubes can inform the search for life beyond Earth. Here, pioneering studies that integrate in-situ DNA sequencing, mineralogical analysis, mass spectrometry, analytical pyrolysis, and high-resolution microscopy to reveal microbial colonisation, biomineral formation, and organic matter preservation in siliceous and sulfate speleothems are presented. This integrative framework was tested during the ESA PANGAEA-X campaign in Lanzarote (Canary Islands, Spain), which demonstrated the feasibility of astronaut-led science using real-time DNA sequencing and handheld geochemistry, marking a leap forward in methodologies for future cave exploration on Mars. Our findings on the Lanzarote lava tubes revealed long-term diagenetic processes influencing the transformation of molecular markers in gypsum speleothems, with implications for the preservation of biosignatures in Mars-analogue settings.
Meanwhile, a once-in-a-lifetime expedition to the remote and protected Selvagens Islands (North Atlantic) further demonstrated the astrobiological analogue potential of volcanic caves. By employing astronaut training protocols, in-situ analyses, portable SEM and autonomous cave exploration, we unveiled a previously unknown microbial biosphere dominated by chemolithoautotrophs and discovered a new cave system, which is now included in the Portuguese catalogue of planetary analogue sites for space exploration.
From wildfires recorded in the siliceous speleothems of Easter Island (Chile) and La Palma (Canary Islands, Spain), to anthropogenic biomarkers trapped in secondary minerals from the lava tubes of Galapagos (Ecuador), we also revealed that these subsurface environments archive not only microbial activity, but also surface-driven, planetary-scale processes and environmental perturbations.
Lava tubes, in this sense, are not only operational laboratories and archives of deep-time biogeochemical dynamics, but also subterranean recorders of land use and ecological changes. As planetary cave science advances from conceptual models to mission-critical strategies, our work helps define both the scientific priorities and technical capabilities needed to identify, characterize and interrogate habitable subsurface environments on Mars and beyond.

Acknowledgements: This work was funded by the Portuguese Foundation for Science and Technology (FCT) through the MICROCENO project (DOI: 10.54499/PTDC/CTA-AMB/0608/2020), by the Spanish Agency of Research (MCIN/AEI/10.13039/501100011033) through the TUBOLAN project (PID2019-108672RJ-I00), and the European Union (Next Generation EU/PRTR funding) grants TED2021-130683B-C21 and TED2021-130683B-C22. The support from the Regional Government of Andalusia through the MICROLAVA project (PROYEXCEL_00185) is also acknowledged.