Assessment of Mars Science and Mission Priorities (2003) / Chapter Skim
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7. Life, Fossils, and Reduced Carbon
7. Life, Fossils, and Reduced Carbon
Pages 54-63
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From page 54... ...
Moreover, it seems likely that life on Mars, if there is any, would take forms similar at some fundamental functional level to microorganisms on Earth, since the same laws of physics as they relate to biological energy transformations and to potentially habitable environments presumably apply on both planets. The subject of life detection in extraterrestrial samples is discussed in a recent study by the Space Studies Board.i Microbes on Earth Microbes are capable of surviving and growing under a broad range of environmental conditions (light intensity; total salinity; pH; temperature; oxygen abundance; carbon dioxide concentrations; water availability; and fluxes of ultraviolet, x-ray, gamma-ray, and highly ionizing radiation)
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From page 55... ...
If so, microscopic fossils of such organisms may be preserved in appropriately ancient sedimentary settings, and the evolutionary descendants of these microbes may inhabit the martian subsurface today. Indeed, if reports are valid of microbes surviving for 25 million to 40 million years encased in amberi9 and up to 100 million years encased in halite crystals,20 it is conceivable that viable biological remnants might be harbored by sedimentary mineral precipitates on the martian surface.
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From page 56... ...
, but not in liquid form.25 Water vapor and ice crystals are present in the atmosphere, and water ice is almost certainly present within the martian regolith at high latitudes and at the surface in polar regions. During the half-year-long, north-polar summer, the water ice present in the residual polar cap warms sufficiently to allow water to sublime into the atmosphere and be distributed globally.
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From page 57... ...
may not have been chosen correctly. Even more importantly, martian life might reside in aqueous oases, such as any recently active volcanic vents or fumaroles distant from the Viking landing sites, or at depths far beneath the surficial regolith sampled by the Viking experiments.
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From page 58... ...
Status of the Search Within the past few years, results of detailed studies have been interpreted as indicating that martian (SNC) meteorite ALH84001 contains possible evidence of biological activity thought to date from about 3.6 billion years ago.42 The possibly biological indicators detected include mineral-zoned carbonate disks and grains of magnetite similar to those interpreted in some terrestrial deposits as being of biological origin, polycyclic aromatic hydrocarbons interpreted to be possible remnants of decayed and geochemically altered biological organic matter, and globular or filamentous microscopic structures thought possibly to be microbial fossils.
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From page 59... ...
These are very significant points that will help to refine thinking about biological issues, but no decisive revelations about martian life can be expected from these missions. Especially if equipped with means for appropriate chemical analyses and imaging at the proposed 30-,um resolution, the rovers hold promise for useful in situ analyses of evaporitic mineral crusts and finely layered hydrothermal and other sedimentary deposits, as well as a search for concentrations of reduced carbon.
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From page 60... ...
· From the 2000 MEPAG report "Mars Exploration Program: Scientific Goals, Objectives, Investigations, and Priorities":47 "Explore high priority candidate sites (i.e., those that provide access to near-surface liquid water) for evidence of extant (active or dormant)
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From page 61... ...
Pederson, "Ecology of Methanogenic Archea in Granitic Groundwater from Hard Rock Laboratory, Sweden," in Proceedings of the Third International Symposium of Subsurface Microbiology, Sept. 15-21, 1996, Davos, Switzerland, Swiss Society of Microbiology, Zurich, 1996.
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From page 62... ...
, "Mars Exploration Program: Scientific Goals, Objectives, Investigations, and Priorities," December 2000, in Science Planning for Exploring Mars, JPL Publication 01-7, Jet Propulsion Laboratory, Pasadena, Calif., 2001.
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From page 63... ...
50. Space Studies Board, National Research Council, "Assessment of NASA's Mars Exploration Architecture," letter report to Carl Pitcher, NASA, November 11, 1998.
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