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Viking Experiment May Have Found Life’s Building Blocks on Mars After All

View of Mars from the Viking lander in 1976. Credit: NASA

A new look at data from the Mars Viking landers concludes that the two landers may have found the building blocks of life on the Red Planet after all way back in 1976. The surprise discovery of perchlorates by the Phoenix mission on Mars 32 years later could mean the way the Viking experiment was set up actually would have destroyed any carbon-based chemical building blocks of life – what the experiment set about to try and find.

“This doesn’t say anything about the question of whether or not life has existed on Mars, but it could make a big difference in how we look for evidence to answer that question,” said Chris McKay of NASA’s Ames Research Center. McKay coauthored a study published online by the Journal of Geophysical Research – Planets, reanalyzing results of Viking’s tests for organic chemicals in Martian soil.

The Viking lander scooped up some soil, put it in a tiny oven and heated the sample. The only organic chemicals identified in the Martian soil from that experiment chloromethane and dichloromethane — chlorine compounds interpreted at the time as likely contaminants from cleaning fluids used on the spacecraft before it left Earth. But those chemicals are exactly what the new study found when a little perchlorate — the surprise finding from Phoenix — was added to desert soil from Chile containing organics and analyzed in the manner of the Viking tests.

“Our results suggest that not only organics, but also perchlorate, may have been present in the soil at both Viking landing sites,” said the study’s lead author, Rafael Navarro-González of the National Autonomous University of Mexico, Mexico City.

The Viking experiment results have been rather controversial over the years. There are some scientists who say the experiment actually did find evidence for life, and others who say the results were inconclusive.

McKay said that organics can come from non-biological or biological sources. Many meteorites raining onto Mars and Earth for the past 5 billion years contain organics. Even if Mars has never had life, scientists before Viking anticipated that Martian soil would contain organics from meteorites.

“The lack of organics was a big surprise from the Vikings,” McKay said. “But for 30 years we were looking at a jigsaw puzzle with a piece missing. Phoenix has provided the missing piece: perchlorate. The perchlorate discovery by Phoenix was one of the most important results from Mars since Viking.” Perchlorate, an ion of chlorine and oxygen, becomes a strong oxidant when heated. “It could sit there in the Martian soil with organics around it for billions of years and not break them down, but when you heat the soil to check for organics, the perchlorate destroys them rapidly,” McKay said.

This interpretation proposed by Navarro-González and his four co-authors challenges the interpretation by Viking scientists that Martian organic compounds were not present in their samples at the detection limit of the Viking experiment. Instead, the Viking scientists interpreted the chlorine compounds as contaminants.

How will we know for sure? The Mars Science Lab mission, with the car-sized rover called Curiosity could help resolve this question.

The Mars Science Lab is going to the Red Planet in 2012, and on board will be the Sample Analysis at Mars (SAM) instrument SAM can check for organics in Martian soil and powdered rocks by baking samples to even higher temperatures than Viking did, and also by using an alternative liquid-extraction method at much lower heat. Combining these methods on a range of samples may enable further testing of the new report’s hypothesis that oxidation by heated perchlorates that might have been present in the Viking samples was destroying organics.

One reason the chlorinated organics found by Viking were interpreted as contaminants from Earth was that the ratio of two isotopes of chlorine in them matched the three-to-one ratio for those isotopes on Earth. The ratio for them on Mars has not been clearly determined yet. If it is found to be much different than Earth’s, that would support the 1970s interpretation.

If organic compounds can indeed persist in the surface soil of Mars, contrary to the predominant thinking for three decades, one way to search for evidence of life on Mars could be to check for types of large, complex organic molecules, such as DNA, that are indicators of biological activity. “If organics cannot persist at the surface, that approach would not be wise, but if they can, it’s a different story,” McKay said.

Journal of Geophysical Research – Planets. (paper not published online at the time of this writing)

Source: JPL

About 

Nancy Atkinson is Universe Today's Senior Editor. She also works with Astronomy Cast, and is a NASA/JPL Solar System Ambassador.

Comments on this entry are closed.

  • Lawrence B. Crowell September 3, 2010, 11:59 AM

    I might be wrong on this, but back in college, some years after the Viking missions, I seem to recall reading that the chemical signatures observed had a diurnal rate. Of course within days after the first data come it the denials about this being the detection of life were sounded. Yet I have thought this diurnal signal should have been taken as a possible signature of biological activity.

    LC

  • sboyd September 3, 2010, 10:16 PM

    instead of ” baking ” the samples. What would be the result if they simply, just added water. Pure and contaminant free of course. I know the result would take a lot longer to become apparent, but is there a chance it might get a different if not more positive result?

  • Lawrence B. Crowell September 4, 2010, 3:18 AM

    The next step beyond the Mars Science Lab would be to have a chemical lab bench capable of a wide range of anlyses. It would require a large chemical store and a sophisticated epindorf robotic system. Microscopes might be in order as well. Of course all of this costs money.

    LC

  • Greg September 4, 2010, 12:07 PM

    This really seems elementary to me. As usual the scientists involved are afraid to draw simple conclusions without evidence. It is obvious now that the methods used by the Viking experiment were flawed and in fact eliminated the very evidence it was looking for. Of course there was no way to predict there would be perchlorates in the soil that would oxidize and destroy any existing organic compounds when heated. Nevertheless this is what the polar lander found and it is not at all a big reach to conclude that these compounds are all over the planet’s soil. After all the whole planet is rust colored, meaning it’s iron is oxidized, and what could it be that is oxidizing it? Plus there are global winds that distribute soil and perchlorates around the planet. And add to that the fact that perchlorate breakdown products were found after the Mars soil was baked by the Viking landers. No more evidence is needde to conclude that perchlorates are uniformly distributed throughout the planet’s soil. NASA has correctly concluded the same and a low heat experiment by the Mars Science Lab will hopefully provide the correct answers to what kinds of organic compounds lie in the soil on Mars.

  • Bravehart September 4, 2010, 7:34 PM

    @ Greg.
    Not so fast, if the perchlorates are of accidic nature or corrosive would that not be
    displayed on the landers? The solar panels and motorwindings would be the first
    to be effected! My suggestion would be that the reason for the “red” color is false!
    When you look at some pictures from satelites have taken from planet Earth, you can see the same false colors at some locations! We have to look at the atmosphere
    to make the analysis (test) credible. Forget the way we do analyze here at home
    because the atmosphere is not the same as over there! The fundamentals are
    different. And we have a nasty habit of looking for a preditermined outcome.
    Adding water to an sample may give an false picture, use the local materials!
    Let the snow/ice melt in a chamber and use that.
    I do know, when I say forget looking for live on Mars or any selastial body
    I would be a dead man but we should be looking for habitual or “fit for human
    consumption” planets? That is our ultimate destination is it not? From what we know about Mars, it does not fit that picture, so stop wasting time, move on.
    Time is of the essence here, we do not have the money or resources to waste!
    I do know that a lot of people make a living “have jobs” playing in the Marsian sandbox but we better move on, that is if we want to live? Our learing curve is long
    and we are forgetfull, when pushed we are smart enough to do great things.

  • Lawrence B. Crowell September 5, 2010, 3:51 AM

    You can’t conclude that life is impossible there as yet. Further, there might have been life in the past or pre-biotic chemistry in the past. So it is possible these signatures could be detected in regions which had water in the past.

    The Martian perchlorates are likely Mg(ClO_4)_2. Perchlorate acid is HClO_4, which in the presence of magnesium gives the oxidative form.

    LC

  • Torbjorn Larsson OM September 6, 2010, 2:54 AM

    Good to have experimental confirmation of what has been suspected since Phoenix.

    @ SBoyd:

    instead of ” baking ” the samples. What would be the result if they simply, just added water. … I know the result would take a lot longer to become apparent,

    I’m not sure what you refer to in that last part, but the baking was done as part of the measurement technique. (Releasing gases to a mass spec for identification; release temperature gives more precise info on the source material (say water release: ice, crystal water, thermal decomposition?).)

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