Ecology of Terrestrial Microbes on a Terraformed Mars
James M. Graham and Linda E. Graham
University of Wisconsin, Madison, WI 53706
The present climate of Mars is characterized by a number of environmental factors that are so extreme they preclude colonization by terrestrial microorganisms. These factors include low average surface temperature (-60C), diurnal temperature ranges up to 100C, intense UV radiation (7x103 ergs.cm-2.s-1) and an atmospheric pressure so low (6-7 mbar) that liquid water is not stable on the surface. Conversely, light levels (max of 860 5mol quanta.m-2.s-1 PAR) are adequate for photosynthetic microbes, bryophytes and many flowering plants. Temperatures in the southern hemisphere are adequate for Antarctic cryptoendolithic microorganisms even now. Moisture levels in the Martian regolith (1-3%) are comparable or greater than those in terrestrial deserts, and the regolith may contain sufficient nitrates to support microbial growth. If the average surface temperature and atmospheric pressure could be raised by such planetary engineering processes as solar mirrors and greenhouse gases (Zubrin and McKay 1996), terrestrial microorganisms could be implanted on the surface of Mars. If pressure rose to 90-300 mbar, diurnal temperature ranges would decrease, and liquid water would be stable. UV radiation would remain a serious limiting factor, but hardy bacteria, lichens and cyanobacteria could survive under rocks or beneath their surfaces. Generation of about 2 mbar of O2 in the atmosphere could create enough ozone to shield the surface from UV radiation (Fogg 1995) and permit a more diverse assemblage of microbial colonizers. Algae and cyanobacteria can grow at high levels of CO2 and generate their own O2 for respiration. They can survive low O2 periods by switching to various anaerobic metabolic pathways. Initial nitrogen cycling would be largely microbial metabolism of regolith nitrates, and recycling of organic nitrogen and ammonia. There appear to be few obstacles to establishing a microbial biosphere on Mars.