Engineering topics

Leschine, S. B.

Publications and source records attributed to Leschine, S. B..

3 records

NASA NTRS1983

Mars - A contamination potential?

Three regions on Mars, Solis Lacus, Noachis-Hellespontus, and the Syrtis Major border areas, would appear to have generally less hostile environments than at the Viking lander sites. Significant soil moisture may extend to within about 1 cm of the surface. Water vapor pressures within the pore spaces may be near saturation, and brines may be physically segregated from pockets of relatively pure H2O. Temperatures reach above 0 C during southern spring and summer, with peak temperatures reaching +22 C. These regions should contain fewer oxidants, and primary synthesis of organics may occur. The potential for contamination of these sites by microbes transported from existing spacecraft should be assessed. The adequacy of proposed new planetary protection procedures for possible future United States Mars Surface Sample Return missions should also be assessed in light of these findings.

Huguenin, R. L.↗

NASA NTRS1981

Comets and the origin of life

The possible role of comets as sites for chemical and/or biological evolution is considered from both the positive and the negative viewpoints. On the negative side, it is pointed out that direct evidence for the chemical composition and size of cometary nuclei is lacking and the thermal history of comets is unknown, so that the length of time that liquid water could have been available ranges from zero to over a billion years. On the positive side, there remains the possibility that there may have been comets which retained liquid water in their interior for a sufficient time and that have more complex molecules than the amino acids and nucleic acid bases found in carbonaceous chondrities, and that the cometary environment may have been more favorable to the origin of life than the terrestrial. It has also been demonstrated that cometary material falls to earth at a significant rate. Problems in understanding the course of chemical evolution on earth may thus have a solution in cometary processes.

Irvine, W. M.↗

NASA NTRS1980

Thermal history, chemical composition and relationship of comets to the origin of life

The role of thermal processes in determining the chemical composition of comets is considered, and implications of possible cometary constituents for the origin and evolution of life on earth are discussed. It is shown that the inclusion of short-lived Al-26 from a nearby supernova explosion into cometary nuclei could lead to comets with surfaces cool enough to retain H2O and interiors warm enough for thermal processing to occur, with the production of complex organic molecules such as amino acids and nucleic acid bases. It is thus suggested that comets may have played a part in seeding the primitive earth with biological polymers capable of self-replication or of evolving towards that capability, and may even be responsible for the subsequent introduction of organic material capable of infecting already existing cells.

Irvine, W. M.↗