Linking biological and geochemical data from Icelandic lava tubes: insights for upcoming missions in the search for extant or extinct life on Mars

J Csuka, S Adeli, M Baqué, I Iakubivskyi, N Kopacz… - 2020 - elib.dlr.de
2020elib.dlr.de
Introduction: The search for extraterrestrial life in our solar system has been pursued most
extensively on our close neighbor, Mars. Early Mars may have been just as hospitable to life
as early Earth, with surface liquid water and a mild climate capable of sustaining microbial
life [1]. Sampling on the Martian surface has thus far not resulted in the detection of any
traces of life, which is unsurprising given the instruments used and the areas sampled,
where ionizing radiation has most likely degraded any signatures of potential past life (see …
Introduction: The search for extraterrestrial life in our solar system has been pursued most extensively on our close neighbor, Mars. Early Mars may have been just as hospitable to life as early Earth, with surface liquid water and a mild climate capable of sustaining microbial life [1]. Sampling on the Martian surface has thus far not resulted in the detection of any traces of life, which is unsurprising given the instruments used and the areas sampled, where ionizing radiation has most likely degraded any signatures of potential past life (see [2] for a review). However, it is possible that microbial life migrated to the subsurface as the surface radiative environment became increasingly harsher. Subterranean environments on Mars would have provided shelter from ionizing surface radiation, a relatively stable internal temperature, and potential entrapment of volatiles, such as water, that may have sustained life. If life was able to flourish in such environments, it or traces of it should still exist in the form of kerogens, permineralized polymers [3], mineral structures or fossils [4], or other geochemical signatures, since the preservation of biosignatures in cave minerals may be stable for many millions of years [5]. Lava tubes form from basaltic flows, typical of pahoehoe eruptions from low lying shield volcanoes. The High Resolution Imagining Experiment (HiRISE), a camera on board the Mars Reconnaissance Orbiter (MRO) launched in 2005, has shown features indicative of lava tube entrances on Mars. The Elysium Mons shield volcano is postulated to have formed in the more habitable time period of Mars, whereas the Tharsis Montes region is potentially too young and was formed after the loss of the magnetic field [6]. This range in the age of lava flows creates a debate on where potential microbial fossils (or life) may lie, but the existence of these lava tubes nonetheless presents a possibility for habitable environments.
Lava caves on Earth are mineralogically similar to caves on Mars, as are the energy sources for life inside, namely redox gradients of iron, sulfur and manganese for example. The chemoautotrophs that feed off of these gradients, and subsequent heterotrophs that feed off of the organic carbon they produce, together form biofilms and microbial mats of incredible complexity. As a consequence, microbes in caves alter their host rocks chemically and induce the dissolution and precipitation of
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