Astrobiological Investigations of Martian Perchlorate and Carbonate Containing Soils
Several remarkable discoveries made by the Mars Phoenix Mission Science Team have recently been described in the press including an alkaline soil pH as well as the presence of both perchlorates and carbonates. These results have shown that either the polar-region soils are quite unique, or else that the global soil unit on Mars has unexpected properties. In light of these ground-breaking new results, and their potentially major impact upon habitability and the design of future experiments to search for life forms on Mars, it is appropriate to assess the implications on astrobiology in a timely and thorough manner.
The primary objective of this work is to experimentally and theoretically model processes that perchlorate and carbonate chemistry may play in the alteration of organic biosignatures on Mars. On Mars, as on Earth, both reaction kinetics and thermodynamic energetics play roles in determining which chemical mechanisms dominate and correspondingly which final products are formed. The parameters that dictate which mechanisms will dominate and are investigated in this work include: perchlorate and carbonate chemistry, the possible catalytic nature of natural components in the soil (especially Fe minerals, and certain other transition elements), water activity, temperature, the details of the soil-organic interface, the oxygen activity in the system, and the presence of other types of oxidizing species such as odd-oxygen and odd-hydrogen species. We also reexamine the Viking chemistry results (GCMS and life detection experiments) in the context of these Phoenix discoveries to establish whether the Viking data sets are consistent with the presence of perchlorate (and related compounds) and carbonates at those two landing sites.
The need for investigation results from the desire to characterize the distribution, lifetime, and chemical state of organic content of soil and soil/ice surface materials on Mars. The likelihood of the successful detection of organic compounds on Mars and the successful interpretation of the significance of the chemical distribution of detected organic compounds is greatly enhanced by an understanding of the rate and nature of any chemical weathering that may be altering compounds of interest. This project directly addresses the NASA Astrobiology Program goal to understand "Planetary Conditions for Life" and NASA Strategic Subgoal 3C "Advance scientific knowledge of the origin and history of the solar system, the potential for life elsewhere, and the hazards and resources present as humans explore space". This project addresses these goals by constraining and extending the understanding of the organic chemical systems and processes that are relevant to the origin, preservation and distribution of organic biomarkers on Mars.