Insensitivity of the Viking GCMS on Mars.

Discussion in 'Astronomy, Exobiology, & Cosmology' started by Exoscientist, Feb 15, 2001.

  1. Exoscientist Mathematician Registered Senior Member

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    The articles in the Special Astrobiology issue of the Proceedings of the NAS are now available free online:

    Possible ecosystems and the search for life on Europa
    Christopher F. Chyba and Cynthia B. Phillips
    Proc. Natl. Acad. Sci. USA, Vol. 98, Issue 3, 801-804, January 30, 2001 http://www.pnas.org/cgi/content/full/98/3/801

    This argues for a possible biosphere on Europa driven by radiation from Jupiter.

    Pre-Global Surveyor evidence for Martian ground water
    Thomas M. Donahue
    Proc. Natl. Acad. Sci. USA, Vol. 98, Issue 3, 827-830, January 30, 2001 http://www.pnas.org/cgi/content/full/98/3/827

    This argues that the deuterium/hydrogen isotopic ratios in the atmosphere of Mars are consistent with recent near surface water on Mars.

    State-of-the-art instruments for detecting extraterrestrial life
    Jeffrey L. Bada
    Proc. Natl. Acad. Sci. USA, Vol. 98, Issue 3, 797-800, January 30, 2001 http://www.pnas.org/cgi/content/full/98/3/797

    This article by Jeffrey Bada discusses the possibility for organics and life on the surface of Mars. It cites the article co-authored by Dr. Bada that tested a Viking GCMS analogue instrument and concluded that millions of microbes per gram could have been missed on Mars:

    Detecting pyrolysis products from bacteria on Mars,
    Earth and Planetary Science Letters, Vol. 185 (1-2)
    (2001) pp. 1-5, http://www.elsevier.nl/gej-ng/10/18/23/101/24/24/article.html [full text]
    (Note: free access to articles on this site ends February 15, 2001.)

    As Dr. Bada says in the PNAS paper:

    "The possible presence of organic compounds on Mars is also uncertain. Using a pyrolysis procedure, in combination with a gas chromatograph/mass spectrometer (GCMS), Viking did not detect any organic compounds above a level of a few parts per billion in near surface samples at two different landing sites (10). However, it is now apparent that the Viking pyrolysis GCMS instruments would not have detected the presence of millions of bacterial cells in 1 g of soil (11). In addition, oxidation reactions involving organic compounds on the Martian surface would likely produce nonvolatile products that also would not have been detected by the Viking GCMS (12)."

    Dr. Bada is also in favor of doing in situ organic tests before samples are returned to Earth, though apparently not because of possible dangers but rather because of the possibility of contamination of the samples:

    "Meteorites from Mars have been extensively investigated to assess whether they contain organic compounds possibly derived from life. Unfortunately, contamination of Martian meteorites by terrestrial organic compounds greatly compromise these investigations (for example, see ref. 13 and references therein). If there is any indigenous organic material present in Martian meteorites, it appears to be derived from the infall of carbonaceous meteorites rather than from Martian biology (14). The problems associated with terrestrial contamination underscores the importance of doing in situ organic compound analyses on Mars before samples are returned to Earth, where even under the best of circumstances they will be exposed to some level of terrestrial contamination."

    It is interesting here that he mentions that analysis of Martian meteorites have shown at least some of their organics appear to be of Martian origin. These include meteorites expected to have been blasted off Mars within the current atmospheric regime. Most significantly he suggests they are of meteoritic origin. This of course was what was expected before the Viking missions. This again underscores the fact that there probably are organics at the surface of Mars that the Viking GCMS was unable to detect. Note as well that Dr. Donahue's article on the Martian atmospheric ratios notes that the isotopic analysis of the Martian meteorites suggest the presence of liquid water that interacted with the Martian atmosphere, that is, surface water. Thus the Martian meteorites indicate both organics and liquid water at the surface of Mars within the current atmospheric regime.

    Barry DiGregorio has mentioned that references to Gil Levin were missing and should have been given in the "Detecting pyrolysis products from bacteria on Mars" paper. References to Gil Levin's prior work suggesting the Viking GCMS could have missed organics on Mars are also missing from this PNAS paper. I agree this omission is indefensible. Dr. Bada had mentioned in an interview that more sensitive detectors should be sent to Mars before human missions are sent to Mars:

    "While life on Mars is of interest to almost everybody, the HEDS program is concerned because of the implications that life on Mars would have for potential human missions to the planet, Bada said.
    "That issue has to be settled pretty much before we send any human explorers there. There is always the fear, although I think it's a very remote fear, that there could be some sort of lethal bug lurking in the martian surface and either we bring it back here and it infects the Earth, or it infects astronauts when they go there,' he said."
    Life on Mars? Before We Go, We've Got To Know http://space.com/news/heds03_mod_991209.html

    Since he discusses the need of further life testing to avoid the possibility of back contamination, Dr. Bada must surely been aware of Levin's concern about missions such as Mars Sample Return. He must also have been aware that those concerns were based on Levin's conclusions that organics could be and in fact probably are at the surface of Mars.
    In addition to this, the PNAS paper discusses methods of detecting an amino acid chiral preference on Mars. However, the methods Dr. Bada proposes can only test for their presence. It is already known that such a preference exists in meteorites, such as the Murchison meteorite. Even if such a chiral preference is observed in possible amino acids on Mars it could be argued they were delivered by meteorites. It is therefore important to note that Gil Levin has developed an update of his Labeled Release experiment that could test for this preference in *active* life:

    THE FUTURE SEARCH FOR LIFE ON MARS: AN UNAMBIGUOUS
    MARTIAN LIFE DETECTION EXPERIMENT, http://cass.jsc.nasa.gov/meetings/marsmet98/pdf/7012.pdf

    Since Dr. Bada discusses such an amino acid chirality as a signature of life it would have been especially appropriate to mention Dr. Levin's proposed experiment in this regard.

    Speculation: why would not Levin's prior work be mentioned? In my opinion it is because he specifically argues in favor of current Martian life. If he had only argued that organics might still exist on the surface his work very well might have been cited. However, because the consensus view of scientists is to relegate Levin's work to the "crackpot" category, any citing of his work that could be seen as supporting his view is resisted, and scientists citing his work would be regarded as "tainting" their own.

    Scientist who take this view are taking what I call an "inverted" view of science. They are saying:

    Conclusion: We KNOW there is no life on Mars.
    Fact 1.: There is no liquid water on Mars.
    Fact 2.: There are no organics on Mars.
    These facts SUPPORT our conclusion of no life on Mars.

    However, note if you take this point of view then even if the supposed facts are disproven they still feel their conclusion still holds.

    However, Gil Levin as a good scientist realizes the actual state of affairs is (or was) this:

    Fact 1.: There is no liquid water on Mars.
    Fact 2.: There are no organics on Mars.
    Conclusion: There is no life on Mars.
    The first two facts lead us to draw the conclusion of no life on Mars.

    Once you look at it this way you are aware that your conclusion is unjustified when your premisses are disproven. Given the recent research suggesting liquid water probably could exist at the surface for short times, the experiments showing the Viking GCMS insensitive to low amounts of organics, and also the fact that positive life signs were detected from the Viking biology experiments, the evidence now favors the biology interpretation rather than not.


    Bob Clark
     

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