Biology
Scientific paper
Jan 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998mmws.work....1a&link_type=abstract
Workshop on the Issue, Martian Meteorites: Where do we Stand and Where are we Going?, p. 1
Biology
Gamma Rays, Mars Surface Samples, Planetary Geology, Radiation Dosage, Sterilization, Bacteria, Viruses, Radiobiology, Cobalt 60, Mars Sample Return Missions, Containment, Rocks, Radiochemistry
Scientific paper
Samples of rock and soil, collected by robotic spacecraft on Mars, will be returned to terrestrial laboratories early in the next century. Plans call for the samples to be placed immediately in biological containment and tested for signs of present or past life and biological hazard. It is recommended that "controlled distribution of unsterilized materials from Mars should occur only if rigorous analyses determine that the materials do not constitute a biological hazard. If any portion of the sample is removed from containment prior to completion of these analyses it should first be sterilized." While sterilization of Mars samples may not be required, an acceptable method must be available before the samples are returned to Earth. Various techniques are routinely used to sterilize biological samples. These include dry heating to temperatures of 150C or higher, heating in the presence of steam, exposure to poisonous gases such as formaldehyde and propiolactone, exposure to H2O2 vapor or plasma, exposure to ultraviolet light, and exposure to gamma radiation. The appropriate technique depends on the physical characteristics of the sample and the desired results. Gamma radiation is routinely used to inactivate viruses and destroy bacteria in medical research. The most commercial sterilizers use Cobalt 60, which emits gamma photons with energies of 1. 173 and 1. 332 MeV. Absorbed doses of approximately 106 rad (104 gamma ray is equal to 104 ergs/gm) are sufficient to destroy most bacteria. The current study is designed to investigate the effects of lethal doses of Cobalt 60 gamma radiation on geologic materials analogous to the first samples to be returned from Mars. The goals are (1) to determine the gamma ray dose required to kill microorganisms within geologic samples, and (2) to determine the effects of lethal doses of gamma radiation on the physical and chemical properties of the samples.
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