Organic Characterization of Mauna Loa Lava Tubes, Hawaii, as Analogs for Mars: Implications for Martian Habitability and Exploration

Abstract:

The search for traces of extant and/or extinct life is one of the driving goals of Mars exploration. Several potentially habitable environments for life have been identified on the planet, including basaltic subsurface lava tubes. While the surface of Mars is currently inhospitable to life as we know it, lava tubes could potentially provide a protected refuge for life or traces of life left behind. Thousands of candidate caves identified on Mars by orbital imaging represent plausible locations for hosting microorganisms and preserving organic biosignatures. Terrestrial subsurface lava tubes are formed by volcanic processes and undergo biogeochemical processes such as exposure to ground water, volcanic gases, sunlight, and microbial activity. In these terrains, some mineral phases are directly related to microbial activity. To hone our ability to detect organic biosignatures and assess the habitability potential of lava tubes, we have been assessing the preservation potential of a terrestrial Mars analog environment, a Mauna Loa lava tube in Hawaii, and evaluating the capability of our current flight instruments to detect organic biosignatures in secondary mineral deposits. In August 2019, several subsurface samples were collected in sections of the lave tube exposed to sunlight and others that remain partly or completely in the dark. The nature and distribution in organic molecules were characterized using pyrolysis gas chromatography mass spectrometry experiments. Our preliminary results indicate a high diversity and abundance of organic molecules in secondary mineral deposits. Combined with mineralogy and metagenomic studies, we show that these organics are likely related to the microbial communities present in the lava tube. Our findings suggest that biosignatures could be uncovered with techniques similar to those onboard current and future martian rover missions, including NASA’s Curiosity rover and ESA’s Rosalind Franklin rover (to land in 2022). We conclude that subsurface basaltic lava tubes are promising targets for astrobiology and are important for the current and future exploration of Mars as well as similar subsurface environments in the Solar System.