BASALTIC CAVES AS ASTROBIOLOGICAL TARGETS ON EARTH AND MARS

Caves are unique biosystems where the protected, stable environment favors secondary mineral precipitation and microbial growth. This combination makes them excellent locations where traces of microbial life, or biomarkers, are recorded in minerals and can be studied in different geographical and temporal settings. Our work in Hawaiian caves has shown an abundance of microbial growth as biofilms and mats on cave surfaces. These microorganisms are intimately associated with diverse secondary deposits of Ca-Mg-carbonates (aragonite, calcite, monohydrocalcite, magnesite, hydromagnesite) and Mg-clay (kerolite) minerals. Textural, chemical and isotopic (C, O) data have been used together to show the role of both abiotic (evaporation, degassing) and microbial (photosynthesis, metal binding) processes in the formation of these deposits. Caves are found in all basaltic provinces on Earth as lava tubes and sea caves. Lava tubes have also been identified on Mars. By analogy, basaltic caves on Mars may contain a record of secondary mineralization that would inform us on past aqueous activity. Martian caves may also provide a habitat for extant microbial life or may provide the best evidence for past life via biomarkers preserved in the cave minerals. This work seeks to study the biogeochemistry of secondary mineral deposits in basaltic caves from three geologically and geographically distinct systems; a year-round sub-tropical climate in young basaltic flows (Hawaii); a temperate climate with cold winters (California); and a tropical climate in older basaltic flows (Deccan and Rajmahal traps, India). More detailed efforts to identify lava tubes on Mars by orbiter data (e.g., Mars Reconnaissance Orbiter) should also be undertaken in conjunction with Earth-based remote-sensing of basaltic areas where caves are known to exist. Results from these studies will help to constrain future exploration targets on Mars and help to define future mission design and infrastructure requirements.