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Project Progress

A source of metabolic energy is a requirement for life, and one likely source of energy to support organisms on Mars is geochemical energy from chemolithoautotrophic reactions. Quantifying the amount of energy produced from chemolithoautotrophic reactions on Mars allows us to determine how much biomass potentially could have existed or exists in the subsurface today. On Earth, microorganisms that obtain energy from inorganic chemical sources and grow solely on CO₂ (chemolithoautotrophs) catalyze redox reactions to make a living. Redox reactions that are energetically favorable but sluggish at low temperatures provide opportunity for microorganism to catalyze the reactions and gain metabolic energy in the process. Chemical energy sources for chemolithoautotrophy arise from disequilibrium in the system, which includes a contrast in oxidation states between strongly reduced basaltic rocks and relatively oxidized seawater. Mars continues to have reduced basalt on the surface and likely had oxidized water at or near the surface in the past.

The objectives of this research are to (1) list probable chemolithoautotrophic reactions that occurred in different environments on Mars, (2) calculate the available energy from each reaction, and as a result, assess the available energy of each specific environment, (3) estimate the amount of biomass that could have been generated at specific types of environments on Mars, (4) determine if these reactions were occurring at biologically useful rates, and (5) compare amount of biomass to analogous systems on Earth.

Within the last year, we have focused on Meridiani Planum, Mars, and assessed its biological potential. The Opportunity Rover was sent to Meridiani because hematite was detected from orbit, and hematite usually forms in the presence of liquid water. Liquid water is a requirement for life, but a source of energy also is required. We have calculated the energy available from redox reactions, including weathering reactions that were likely to have occurred at Meridiani. Redox reactions include sulfide oxidation, iron oxidation, sulfate reduction, and iron reduction. Weathering of minerals such as fayalite, hematite, epsomite, and pyrite also release geochemical energy for microorganisms to take advantage of. We used Geochemist’s Workbench to model the mixing of reduced basalt with oxygenated water in equilibrium with a martian atmosphere in order to get an idea of dissolved compound concentrations (e.g. Fe²⁺, Fe³⁺, SO₄^2-, HS^-, etc.). The energy available from each reaction was then used to calculate the amount of biomass that could be supported per gram of primary rock.

In the near future, we plan to expand this research to other types of environments on Mars. For example, we plan on estimating the amount of biomass that could have been produced from shallow lakes, basalt aquifers, impact induced hydrothermal systems, and acid saline lakes. All of these environments are likely to have been present on Mars, so we must understand if these different types of environments produce sufficient energy to support ecosystems. We can then compare the estimated biomass production on Mars to known terrestrial values. We also plan to look at the kinetics of each reaction. This is an important aspect because there is a major difference between the total energy available and the rate at which the energy is available. If these reactions are taking place on Mars at very low temperatures (0C), then studying the kinetics of these reactions is very important in order to understand how fast or slow energy may be made available to potential biomass. Even if the rates of the reactions are slow because of the low temperatures, microorganisms can still catalyze the reactions and gain metabolic energy.