Pathfinder is now enroute to Mars for a July 4, 1997 landing. Its lander is equipped with a camera having better color and spatial resolutions than did Viking’s. It is possible that a close-up picture of a rock might show clear evidence of biological colonies. A search for such evidence should be a Pathfinder priority.
2. Use Hubble Telescope. The Hubble Telescope should be used to seek evidence of large areal changes in the color and patterns of the martian surface and seek to correlate them with atmospheric water vapor and climatic seasons. Useful images that already may exist in the Hubble files should be compared.
3. Seek Chirality in Mars Samples. Perhaps the surest robotic means for unequivocal distinction of biological from chemical reactions is a test for chiral activity. For some yet unknown reason, or by chance, when the first living cells came into existence their enzymes were chiral specific. They catalyzed protein-building reactions with L-amino acids only. They had a similar preference for L-carbohydrates over D-forms. Throughout the evolution of all living forms, these preferences have been genetically transmitted. This peculiarity of living systems provides a ready means of distinguishing them from chemical reactions. Chemical reactions, without the intervention of man, cannot distinguish between L- and D-isomers. On the other hand, all known life forms utilize and make virtually only the L-form of amino acids. Thus, were a sample of martian soil to react with one chiral isomer of a compound and not the other, the biological nature of the reaction would be established. A simple, small, low-cost experiment has been proposed90 which would separately add L-cysteine and D-cysteine (FIG. 11) to respective small ovens in the Surveyor ’98 Thermal and Evolved Gas Analyzer (TEGA). TEGA will measure CO2 evolved when samples of martian soil placed in them are heated. Were the amount of CO2 evolved from the oven containing one isomer of cysteine to exceed the amount from the oven containing the other isomer significantly, the case for life would be confirmed.
4. Protect Health and Environment. Samples of martian material should not be returned to Earth before a thorough evaluation of possible hazards. The simple test for chirality could provide a warning of potential hazards to health and environment before a sample from Mars is returned to Earth. An upgraded version of the LR experiment might be added to an upcoming martian lander. This experiment would differ from the original in that the chiral isomers would be offered separately. The advantages of this approach are that it builds on the proven technology of Viking and that the Viking results provide relevant data for comparison. In addition, it could permit testing under controlled environmental conditions. Many other means of inquiry would follow a positive test to begin studies of comparatively biology.
5. Continue SNC studies. The ongoing appraisals of the meteorites reported to contain evidence of martian microbial life may confirm the conclusion reached herein. In particular, if EETA79001 is validated as to both its Mars origin and its evidence of microbial life, this would constitute such confirmation.
ACKNOWLEDGMENTS
In the 45 years since I first developed the radioisotopic method for detecting microorganisms, I have been fortunate in my assistants. This variously composed team total nearly half a hundred people. I have acknowledged each in the more than 50 published papers many have co-authored with me, and I now thank them collectively. I do want to mention several individuals. Dr. Patricia Ann Straat, my Viking Co-Experimenter, was my right arm at Biospherics during the 10-year period covering the Viking mission. She was essential to the success of the LR experiment. Her predecessor was Mary-Frances Thompson who did a splendid job overseeing our early laboratory efforts. Engineer George Perez was able to take my sketchy concepts for the early instruments and reduce them to excellently functioning metal. TRW, Inc. converted the early instruments into the faultlessly performing Viking LR instruments. I particularly want to thank my son, Dr. Ron Levin, a physicist, for his constant support of the LR life interpretation, his help with the water-on-Mars issue, and in extracting the Mars images from the JPL tapes.
The bulk of the work reported on herein was funded by a series of NASA Headquarters contracts with the companies where I was employed: Resources Research, Inc., Hazleton Labs, Inc., and Biospherics Incorporated. Since 1979, my efforts in analyzing the Viking Mission results have been supported by Biospherics. I would like to thank its Board of Directors for indulging my commitment to this issue and for the funds required.
REFERENCES
1. McKay, D.S., E.K. Gibson, K.L. Thomas-Keptra, H. Vali, S. Romanek, S.J. Clemett, X.D.F. Chillier, C.R. Maechling, and N. Zare, “Search for Past Life on Mars: Possible Relic Biogenic Activity in Martian Meteorite ALH84001,” Science, 273, 924-930, 1996.
2. “Martian Lanuch Pads,” S&T’s Weekly News Bull., Sky Pub. Corp., 1, 11, Nov. 96.
3. Levin, G.V.,” Detection of Metabolically Produced Labeled Gas: the Viking Mars Lander,” Icarus, 16, 153-166, 1972.
4. Levin, G.V. and P.A. Straat, “Labeled Release – An Experiment in Radiorespirometry“, Origins of Life, 7, 293-311, 1976.
5. Miller, S.L., “A Production of Amino Acids Under Possible Primitive Earth Conditions,” Science, 117, 528, 1953.
6. Levin, G.V. and P.A. Straat, “A Reappraisal of Life on Mars,” Proc.. NASA Mars Conf., Nat. Ac.