CHARACTERIZING BULK ORGANICS IN THE DEEP ROCK SAMPLES FROM THE MARS ANALOG RIO TINTO EXPERIMENT: AN ANALOG FOR THE SEARCH FOR DEEP SUBSURFACE LIFE ON MARS

The subsurface is the key environment for searching for life on planets lacking surface life. Subsurface ecosystems are of great relevance to astrobiology including the search for past/present life on Mars. Conditions on the Martian surface do not support biological activity but the subsurface might preserve organics and host subsurface life [1]. A key requirement for the analysis of subsurface samples on Mars is a set of simple tests to determine if the sample contains organic material of biological origin, and its potential for retaining definitive biosignatures. To date, the only reported microbial ecosystems thriving at home no-oxygen/ no-sunlight conditions derive energy from hydrogen evolved in the decomposition of basalt [e.g., 2]. Searching for subsurface life based on Fe and S minerals that are ubiquitous on Mars has been the Science objective of the Mars Analog Rio Tinto Experiment (MARTE).

MARTE is performing deep drilling of cores in a volcanically-hosted-massive-sulfide deposit at Rio Tinto, Spain, an important analog of the Sinus Meridiani site on Mars. Results from MARTE suggest the existence of a relatively complex subsurface life including aerobic and anaerobic chemoautotrophs, and strict anaerobic methanogens sustained by Fe and S minerals in anoxic conditions, which is an ideal model analog for a deep subsurface Martian environment.

We report here on the presence of bulk organics (C-org: 0.03-0.05Wt% and N-tot: 0.01-0.04Wt%) in weathered tuffs, gossan, oxidized and fresh pyrite stockwork, from a Rio Tinto borehole into massive sulfide. Inorganic carbon is up to 0.50-0.77Wt%.

Assessing the amount of C-org and N available throughout the RT subsurface brings key insight on the type of trophic system sustaining its microbial ecosystem (i.e., heterotrophs vs. autotrophs) and the biogeochemical relationships that characterize new type of subsurface biosphere at RT. This potentially novel biosphere on Earth could be used as a model to test for extant and extinct life on Mars.

Further work is underway to draft relationships among the distribution and source of organics, i.e., in situ vs. fossil, and mineralogical, and microbiological dataset available from the MARTE Team Members.

[1] Boston, P.J., et al., 1992. Icarus 95,300-308; [2] Stevens, T.O. et al., 2000. Environ. Sci. Technol. 34:826-831.