Sources of nutrients and energy for a deep biosphere on Mars

A Conspicuous Clay Ovoid in Nakhla: Evidence for Subsurface Hydrothermal Alteration on Mars with Implications for Astrobiology

“…It is also possible that the biologically mediated reduction of FeS by H 2 that could potentially occur in this type of subsurface environment (i.e., FeS + H 2 S/FeS 2 + H 2 ; Fisk and Giovannoni, 1999) seems to parallel the geochemical conversion of pyrrhotite to marcasite that we observed here. Inorganic compounds such as H 2 O, SO 2 , CO 2 , and O 2 , as well as several simple organic compounds, have now been detected in the Rocknest eolian deposits (upon heating) by instruments on the MSL Curiosity rover (Leshin et al, 2013), increasing the likelihood that some other biologically important chemicals may also exist and be available for transport in hydrothermal fluids in the martian subsurface.…”

“…In this case, the bacteria act as substrates onto which clay minerals and iron oxyhydroxides form, some of which resemble the ovoid structure described here, both in terms of morphology and mineralogical makeup, demonstrating that hydrothermal fossilization of microorganisms is possible in these environments (Geptner et al, 2005). Moreover, redox reactions often take place inside such tiny volumes (Geptner et al, 2005), which, along with the occurrence of certain types of mineral surfaces, might provide the organisms with the required energy for their metabolism (Fisk and Giovannoni, 1999;Varnes et al, 2003).…”

“…All the required chemicals necessary for autotrophic or chemolithotrophic microorganisms are available on Mars (Fisk and Giovannoni, 1999), such as H 2 , CO, CO 2 , CH 4 , Fe 2 + , Mn 2 + , H 2 S, and S-chemicals likely to have also been available in the vicinity of the ovoid. It is also possible that the biologically mediated reduction of FeS by H 2 that could potentially occur in this type of subsurface environment (i.e., FeS + H 2 S/FeS 2 + H 2 ; Fisk and Giovannoni, 1999) seems to parallel the geochemical conversion of pyrrhotite to marcasite that we observed here.…”

“…Nakhla has already yielded abundant evidence that some of these key conditions exist (or have existed) on Mars and therefore provides evidence for a protected subsurface environment on Mars that could potentially preserve evidence of microbial life. Consequently, in this section we consider the possibility that fractures and cavities in the Nakhla parent rock might once have hosted microbial life, especially given that, on Earth, a variety of redox reactions that take place in such environments are often mediated by microorganisms (Fisk and Giovannoni, 1999;Varnes et al, 2003). The potential that a microbial ecosystem may have developed in the martian subsurface seems increasingly plausible, and recent studies have identified some localities on Mars (e.g., McLaughlin Crater) that might preserve evidence of a deep biosphere associated with subsurface aquifers (Michalski et al, 2013).…”

Archaeal diversity analysis of spacecraft assembly clean rooms

“…Due to this ubiquity and metabolic diversity, Archaea are considered by some to be capable of surviving, or even thriving, on Mars (Krasnopolsky, 2006). The potential discovery of (ancient) liquid water on Mars (Herkenhoff et al, 2004) and the chemical compositions of the Martian atmosphere (Weiss et al, 2000) and crust (Fisk and Giovannoni, 1999) not only raises the possibility that life may have or may still exist there, but indicates that conditions capable of supporting terrestrial life may also be present. The prevention of contamination of Mars and other extraterrestrial environments with terrestrial biomolecules and/or life (Rummel, 1989) is therefore tremendously important to avoid confounding future life detection missions and preserve the pristine conditions of other solar bodies.…”