Biological Contamination of Mars Issues and Recommendations (1992) / Chapter Skim
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APP D: EXCERPTS FROM THE 1978 REPORT
APP D: EXCERPTS FROM THE 1978 REPORT
Pages 82-102
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From page 82... ...
* Reprinted from the Space Science Board, National Research Council, 1978.
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From page 83... ...
. The report established the minimum conditions necessary to define a microenvironment on Mars that would support growth of the most "hardy terrestrial organisms." The conditions established were the following: (a)
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From page 84... ...
Table 1 makes that comparison in abbreviated form. Appendix A discusses in fuller form the inferences that can be drawn from the Viking findings about those physical and chemical characteristics of the Martian surface that are pertinent to the question of the growth of terrestrial microorganisms.
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From page 85... ...
A Subpolar Regions within about 6 Centimeters of the Surface Our conclusion is that no terrestrial organisms could grow within a few centimeters of the surface in the regions lying between the two residual polar caps.
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From page 86... ...
None of this new information suggests that the Martian surface is less harsh to terrestrial microorganisms than was thought prior to Viking.
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From page 87... ...
In the southern hemisphere, the maximum temperature at a depth of 24 cm is estimated to be -35°C, still 20° below the minimum terrestrial growth temperature.4,8 At increased depths there is an increased likelihood of encountering ice, the existence of which would enhance the possibility of liquid water. But water that is liquid below -20°C and is in equilibrium with ice has an activity ( w)
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From page 88... ...
that have higher temperatures. -- Although there is extensive information on the minimum growth temperatures of terrestrial microorganisms, the remote possibility exists that some unknown organism has a growth minimum below -15°C.
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From page 89... ...
One consequence of these lethal conditions is that our recommended value of <10-7 for Pg in the residual polar caps applies only to terrestrial organisms that are released directly in that region. The Pg for organisms transported into the polar caps from the subpolar regions would be orders of magnitude lower.
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From page 90... ...
The limiting conditions listed in Table 2 for terrestrial life are not the limits for conceivable life elsewhere. There is fairly wide agreement that life, if it exists elsewhere, is based on carbon chemistry and that it requires nitrogen; organic compounds of high information content, energy, and substrates to permit the synthesis of the organic compounds; and liquid water.
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From page 91... ...
IV. CONCLUSIONS PERTINENT TO THE CURRENT VIKING ORBITERS As of August 1977, two years have elapsed since the unsterilized Orbiters were launched from earth.
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From page 92... ...
V QUARANTINE STRATEGY FOR FUTURE MISSIONS TO THE MARTIAN SURFACE Our Committee has recommended that the next phase in the biological exploration of Mars should be to acquire and characterize soil samples from areas likely to contain sediments and ice-regolith interfaces.1 Locating these areas and locating sites that are shielded from the powerful atmospheric ultraviolet radiation and the powerful surface oxidants will require subsurface sampling by a soft lander, by penetrators, or by both.
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From page 93... ...
If so, a limiting factor with respect to the allowable microbial burden on a soft lander would likely become the avoidance of contaminating the metabolic experiment by terrestrial microorganisms.
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The probability for the existence of liquid water anywhere on the planet remains low. The surface temperatures and atmospheric pressures preclude the existence of pure bulk liquid water under equilibrium conditions.
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From page 95... ...
This is below the minimum growth temperature of most terrestrial microorganisms, although, as discussed later and in Appendix B, a few terrestrial organisms can grow at temperatures as low as -14°C. In the southern hemisphere of Mars, the maximum summer surface temperatures may reach 20°C.4 At night, even in summer, the temperature drops to -83°C.
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From page 96... ...
But even if trace amounts of organic compounds are in fact present in the soil of the landing sites, the probability is remote that these would provide a nutrient medium that could be used by terrestrial microorganisms (see Reference 3 for further discussion)
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From page 97... ...
Estimates from the infrared thermal mapper (IRTM) indicate that the maximum surface temperature will fall below -15°C (the minimal terrestrial growth temperature -- see Appendix B)
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From page 98... ...
In the southern hemisphere as a result of the eccentricity of the Martian orbit, the maximum surface-.temperatures between latitudes 5° and 45° are about 15° warmer than at the present landing sites. As a result, at subsurface depths sufficient to damp out diurnal variations, the maximum summer temperature is calculated to be about -35°C, still some 20° below the minimum confirmed terrestrial growth temperature.4 C
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From page 99... ...
to have much bearing on their current suitability for the growth of terrestrial organisms, except that they might possibly contain concentrated deposits of electrolytes and organic compounds. The orbital infrared temperature and water-vapor measurements also show heterogeneities, but again none of those detected have properties significantly more favorable to terrestrial life than do the largerscale features.
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From page 100... ...
This inability of organisms to grow below about -15°C is consistent with the known physical state of aqueous solutions at these temperatures. As Table B.1 shows, when solutions of sodium chloride in water, for example, are equilibrated at various subzero temperatures, the concentrations in the unfrozen portions exceed 4 molal below -15°C.
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From page 101... ...
FIGURE B.1 Reported cases of microbial growth below 0°C. (Adapted from Reference 15.)
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From page 102... ...
below the value permitting the growth even at optimal temperatures of all microorganisms save halophilic and osmophilic forms. As shown in Table B-1 and Figure B-2, the values of aw at -14, -16, -18, and -20°C are 0.87, 0.85, 0.84, and 0.82, respectively.
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