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Viking Data Still Cause Stir About Mars Life
By Michael Paine
Special to SPACE.com
posted: 01:00 pm ET
05 September 2001
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Later acts
Rick Cavicchioli of the University of New South Wales studies extremophiles from Antarctica, including an organism called Methanogenium frigidum. It only grows in very cold oxygen-free conditions and makes a living by combining hydrogen and carbon dioxide to produce methane. Other Methanogens have been found in warmer conditions such as deep sea hydrothermal vents but the Antarctic bugs will die if exposed to oxygen or to temperatures higher than 18 degrees Celsius. They stop growing at temperatures below -10 degrees Celsius but might do quite well in the soils of Mars on a warm day, if they could find a source of hydrogen and protection from UV rays. Cavicchioli points out that M. frigidum do not require a source of carbon, other than carbon dioxide in the air. They are therefore unlikely to have been interested in the offer of carbon-containing broth in the LR experiments.
Joe Miller of the Keck School of Medicine at the University of Southern California has taken a different approach to analysis of the Viking LR data. He noticed that the radioactivity readings had a small but persistent sawtooth pattern that matched the length of the Martian day. This caught his attention because he had observed similar "circadian rhythms" in Earthly microorganisms. Careful analysis revealed that the fluctuations matched those of the temperature in the test chamber. The Viking laboratory was designed to hold the samples at near constant temperature despite the fluctuations of more than 50 degrees Celsius outside between the Martian day and night. The equipment managed a creditable 2 degrees Celsius fluctuation but Miller points out that this was still sufficient to cause some of the observed oscillation in radioactive gas due to reabsorption of carbon dioxide when the soil cooled slightly. He claims that this effect, together with other sources of variation such as equipment effects, can, at best, account for between 55 percent and 78 percent of the observed LR oscillation. He suggests that a biological response best explains the remaining component of the oscillation and several other characteristics of the experiments.
Miller is conducting further analysis of the Viking LR data to look for circadian rhythms that do not match the length of the Martian day, and therefore the temperature fluctuations in the chamber. He notes that Earthly organisms that are held under constant conditions develop rhythms that are out of step with day and night on Earth.
Miller is particularly excited about the possibility of organisms that process methane on Mars because methane is not easily absorbed by soil. The sawtooth pattern would need to be explained by other means. Also, from Earthly findings, it now seems possible to have an ecology of methane producers and methane consumers that live in a symbiotic partnership in the absence of oxygen.
While the work of Miller and Levin, if confirmed, might push the pendulum further towards biology it is unlikely that the Viking data will ever fully eliminate the possibility that the strange results were caused by exotic chemical reactions. It seems that we will need to wait for further spacecraft missions to Mars to resolve the question of whether the Viking experiments detected life. Hopefully the designers of those spacecraft are looking at the lessons learned from the stunning Viking project.
Bibliography
Cavicchioli, R., Thomas, T., Saunders, N., Curmi, P., Kuczek, E., Slade, R., Davis J. and Mattlick, J. (2000) :Towards the genome of the psychrophilic archaeon Methanogenium frigidum', Proceedings of the 8th International Conference on Small Genomes, 2000. http://www.micro.unsw.edu.au/rick/arrowhead.html
Horowitz, N. (1977) 'The Search for Life on Mars', Scientific American, November 1977.
Kimball, J. (2001) Is (Was?) there life on Mars, http://www.ultranet.com/%7Ejkimball/BiologyPages/M/Mars.html
Klein, H.P. (1996) 'On the Search for Extant Life on Mars', Icarus 120, 431-436, 1996.
Klein, H.P. (1998) 'The Search for Life on Mars: What we learned from Viking', J. Geophysical Research Vol 103, No E12 28463-28466, 25 Nov 1998.
Klein, H.P. (1999) 'Did Viking discover life on Mars?', Origins of Life and Evolution of the Biosphere, 29: 625-631, 1999.
Levin, G.V. (1997) 'The Viking Labeled Release Experiment and Life on Mars', Proceedings of SPIE Conference, 1997.
Levin, G.V. and Straat, P.A. (1977) 'Recent results from the Viking Labeled Release Experiment on Mars', J. Geophysical Research Vol 82 No 28, 30 Sep 1977.
Levin, G.V., Kuznetz, L. and Lafleur A. (2000) 'Approaches to Resolving the Question of Life in Mars', Proceedings of SPIE Conference, 2000.
Madigan, M.T. and Marrs B.L. (1997) 'Extromophiles', Scientific American, April 1997.
Miller, J.D., Straat, P.A. and Levin G.V. (2001) 'Periodic Analysis of the Viking Lander Labeled Release Experiment', Proceedings of SPIE Conference, 2001.
Scientific American, editors (1977) 'Science and the Citizen: Ambiguities of Mars', Scientific American, February 1977.
Space Studies Board (2000) Evaluating the Biological Potential in Samples Returned from Planetary Satellites and Small Solar System Bodies, http://www.nas.edu/ssb/sssbch1.htm | | | |
