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2 THE POSSIBILITY OF EXTANT LIFE ON MARS
Pages 10-16

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From page 10...
... During the half-year-long north-polar summer, the water-ice residual polar cap heats up enough to allow water to sublime into the atmosphere and be distributed globally. The polar surface temperatures are too low, however, for the ice to melt.
From page 11...
... Analytical experiments carried aboard the Viking landers indicated that the surface environment of Mars is highly oxidizing, although the exact nature of the oxidants was not determined (Hunter, 1979~. It is possible that the martian soil contains oxidants, such as hydrogen peroxide, which are postulated to form photochemically from atmospheric water vapor and to diffuse readily into the soil.
From page 12...
... The source of organic molecules could be external for example, organic molecules formed in interplanetary space and supplied to Earth along with meteoritic dust and debris that accreted onto Earth, or terrestrial, formed by chemical reactions in Earth's environment. Transient evaporating ponds, hydrothermal vents where water circulates beneath the surface near volcanic intrusions, and the surfaces of clay minerals that could provide stability and order to long chains of molecules have all been postulated as candidate environments where prebiotic chemistry may have undergone a transition leading to self-replicating entities.
From page 13...
... The evidence is derived from the form of the valley networks that involved liquid water, as discussed above; catastrophic flood channels that indicate the presence of water reservoirs in the crust; morphologies such as rampart crater ejecta and lobate debris aprons that might be indicative of nearsurface ice; and, of course, the polar caps, which contain substantial quantities of water. Given the extensive evidence for both heat sources and accessible water, it is likely that hydrothermal systems have been present throughout martian history.
From page 14...
... Such life forms could survive in occasional localized ecological niches. Such niches could be liquid water or hot springs associated with extrusive and intrusive volcanism or liquid water buried deep beneath the surface where it is stable.
From page 15...
... The Viking experiments were able to test for only a couple of the possible mechanisms by which putative martian organisms might obtain energy; these involved the utilization of either carbon dioxide or extant organic molecules as a source of carbon in the production of organic molecules. Putative martian biota might employ other mechanisms to obtain energy and might do so under physical conditions quite different from those of the Viking biology experiments.
From page 16...
... Thus, there are plausible scenarios in which a sample returned from Mars could contain living organisms, either active or dormant.


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