The 1976 Viking missions to Mars have been our only attempts to date to search directly for life on another planet. The pair of identical Viking landers carried a trio of life detection experiments that were a marvel of early 1970s-era miniaturized technology. In addition, a gas chromatograph-mass spectrometer (GCMS) was carried to analyze the vapors released during heating of a sample to detect any organic compounds in the Martian soil. Unfortunately the scientific results of the Viking life detection experiments were ambiguous at best. While there was activity observed in all the life detection experiments with activity in one in particular (i.e. the LR or Labeled Release experiment) giving a positive result based on protocols established before the Viking flight, the lack of any detectable organic compounds in the Martian soil cast doubt on this interpretation.
Model of the Viking lander at the Smithsonian National Air & Space Museum. The two Viking landers which reached Mars in 1976 were the only spacecraft to ever perform experiments to directly search for life on another planet. (A.J. LePage)
The consensus of the planetary science community was that Viking did not detect life on Mars and that the activity observed in the life detection experiments was due to simple, abiotic chemistry. Scientists hypothesized that some sort of powerful oxidant generated by the high UV flux and hyperarid conditions on the Martian surface was responsible for the observed activity instead. But after almost a third of a century of observations, laboratory experiments and debate, it was NASA’s Phoenix mission to Mars which seemed to finally identify the long sought oxidizing agent in 2008: a highly reactive family of compounds called perchlorates.
Unfortunately, the identification of perchlorates in the Martian soil only complicated matters further. The rejection of a biological explanation for the apparent positive results from Viking’s Labeled Release experiment and the unusual activity in the other experiments back in 1976 was based in part on the lack of any detectable organic compounds in the soil. Unfortunately even if organic compounds were present, they would have been destroyed when the Viking GCMS heated its soil samples in the presence of the perchlorates to produce carbon dioxide, water vapor and traces of other gases including chlorinated hydrocarbons which had been detected by Viking but were dismissed at the time as being just traces of cleaning agents used on the instrument before launch. While Phoenix and NASA’s Curiosity rover, currently exploring Mars, have been equipped with more sophisticated instruments to detect organic compounds on Mars, their efforts have been complicated by the presence of these perchlorates. And the more complex task of detecting life on Mars has not been directly addressed by any Mars mission since Viking.
Just a few days ago, I received my June 2014 issue of Scientific American and discovered a great article: “How to Search for Life on Mars” by Christopher P. McKay of NASA Ames Research Center and Victor Parro Garcia of the Center for Astrobiology in Spain. The authors, in addition to addressing the complications of the presence of perchlorates in the Martian soil, contend that the Viking life detection experiments were flawed from the start. These experiments, which had been developed back in the 1960s, used culture-based methods which are no longer considered definitive in detecting life even in terrestrial soil samples since only a small fraction of microbes can be grown in a culture. In this article, McKay and Garcia outline modern approaches to life detection experiments that rely on determining the presence of key biomarkers in the soil. Although there still remains the question of which of the multitude of potential biomarkers should be sought, these techniques are now advanced enough that instruments employing these new methods could be built and included in future Mars lander or rover missions. And while the authors were focused on the search for life on Mars in this article, these methods could also be applied to search for life or its traces in other biocompatible environments elsewhere in the solar system.
This article is well worth reading and I highly recommend it.
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Video
Here is a 1978 NASA documentary on the Viking science results (narrated by Viking Science Team member, the late Harold Masursky, if I am not mistaken) called “19 Minutes to Earth”. The video was originally produced for use in high school science classes and is definitely a product of the late 1970s but it is still a good review of the Viking science results that is worth viewing.
Related Reading
“Automated Biological Laboratory”, Drew Ex Machina, August 7, 2014 [Post]
“Viking and The Question of Life on Mars, Part 1”, SETIQuest, Volume 3, Number 3, pp. 1-6, Third Quarter 1997 [Article]
“Viking and The Question of Life on Mars, Part 2”, SETIQuest, Volume 3, Number 4, pp. 1-7, Fourth Quarter 1997 [Article]
General References
Christopher P. McKay and Victor Parro Garcia, “How to Search for Life on Mars”, Scientific American, Vol. 310, No. 6, pp. 44-49, June 2014 [Article Access]
You state: ” ..with activity in one in particular (i.e. the LR or Labeled Release experiment) giving a positive result based on protocols established before the Viking flight..” and later “..which seemed to finally identify the long sought oxidizing agent in 2008: a highly reactive family of compounds called perchlorates..”
The problem here is: perchlorates are proven to be not reactive under the conditions of the (Viking-) labeled release experiment and its positive results for life detection. So the active agent of the Viking LR has NOT been identified as inorganic compound to date while the problems of the none-detection of organics in the Viking GCMS tests could very well be explained by the presence of perchlorates. So still the biologic solution of the Viking LR remains a viable solution for the LR results.
regarding McKay: in my opinion he is wrong in stating the Viking biology experiments were all flawed – they may have been to narrow focused on things we knew by that time but what else should they have done in the 70ies? Surprisingly they may have even stumbled across something with a restricted set of tests? No guts, no glory!
Of course Mckay needs to advertise his own research which is interesting also. 😉
I greatly appreciate your comments and realize that there is much disagreement in some quarters about the interpretation of the Viking experiments. Personally I am troubled by the fact that the activity observed in the Viking life detection experiments (especially the LR) was dismissed as simple chemistry 30-some years ago based in large part on the non-detection of organic compounds by the GCMS. Now that non-detection is explained by the presence of perchlorates which calls into serious question the logic of this original argument. That being said, I was unaware that perchlorates can not explain the activity observed in the Viking LR experiment (whose results I have always felt were the most difficult to explain away as non-biological, if you had read my earlier work on this subject). If you could cite a paper in a peer-reviewed publication that supports this claim, it would be most appreciated.
Thanks – Drew LePage
After the Phoenix discovery of perchlorates in arctic soil on Mars (and recent findings suggesting perchlorates in Gale crater as well), most scientist working on that subject concentrated on the implications for the Viking GCMS test for organics (i.e. the well known Navarro-González; McKay papers et cetera). Therefore -as far as I know- no (peer-reviewed) papers dealing directly with perchlorates and the Viking LR results other than the suggestion of radiolytic decomposition products of perchlorate as a possible active agent in the LR and the other biology tests.
Nevertheless it is well known that perchlorate salts as such wont react/decompose at lower temperatures as is on Mars. In the following paper the decomposition/reaction/combustion temperature of magnesium-perchlorate and derivates (main consensus is that this kind of perchlorate has been detected by Phoenix and MSL) has been found starting from no less than 244 degree C, that means the LR control regimen temperature of 160 degree C wont have affected the perchlorate in the active sample and those wont have destroyed the active agent as happened in the LR control results (both landing sites) if it were said perchlorates. http://pubs.acs.org/doi/pdf/10.1021/j100697a010
Also perchlorate salts wont vanish due to prolonged storage in a sample preparation chamber at approximately ambient conditions as happened to the active agent of the LRx on Mars. On the other hand, microbes isolated from there native environment in the dark would likely not survive such a treatment.
My personal opinion and that of most of my biologist peers from European Universities and research facilities with is that G. Levin may well be right with his claim that the LR indicated extant microbial life on Mars.
The ExoMars mission – if successful – might shed more light on this and is highly anticipated by us!
Sorry for the somewhat clumsy writing – English is not my main language. 🙂
No apologies needed… I don’t read English very well this early before my morning coffee 😉 In any case, I greatly appreciate the the additional commentary and especially the link to a peer-reviewed paper on the subject of perchlorate chemistry. If you haven’t done so already, you should check out an earlier, detailed article I did on this subject cited above in the Related Reading section, “Viking and The Question of Life on Mars”. Part II of that article deals in part with Gilbert Levin’s work during the 1980s an 1990s to prove that his LR experiment was more sensitive to the presence of microbes than any of the other instruments and that the LR had indeed detected life on Mars. Of course in the end, more investigations are needed on this topic and experiments on ExoMars and other missions will hopefully help resolve this question.
Once again, many thanks!
Drew LePage
Thanks for the informative article.
Bob Clark