≡ Menu

Reconsidering Viking on Mars

The day the first Viking lander touched down on Mars is still fresh in my memory, particularly the early confusion about the real color of the Martian sky (which had seemed, by data misinterpretation, to be a rich blue). Then the excitement about possible life through experiments combing through the top few inches of Martian soil. Bob Schieffer announced there may be life on Mars — “no fooling”, said Schieffer with a delighted grin — on CBS news not long after, but later studies discounted the one experiment that might have detected biological activity.

Gil Levin, the scientist in charge of the disputed Viking experiment, still thinks it was successful. But other experiments could find no organic molecules in the Martian soil, an assumed prerequisite for life. Now a new paper argues that the Viking methodology was flawed. In fact, similar experiments don’t even find organic molecules in the Atacama Desert between Chile and Peru, where dry conditions seem conspicuously Mars like, and where experiments on remote life detection have continued at a robust pace. Yet updated testing reveals carbon at these sites.

And Rafael Navarro-González (National Autonomous University, Mexico) says in the new study that if the Viking scientists had known these results thirty years ago, they would have interpreted Viking’s work differently. Which is not to say that Viking detected life, but that we can’t discount organic molecules in the soil, which probably houses 1,000 times as many organic molecules as Viking data suggested.

Add to that finding Neill Reid’s recently published work on one-celled organisms from Antarctic lakes and we’re talking about living things in conditions that mimic what we should find on Mars. So let’s not rule Mars out; if bacteria can live almost two miles below the Earth in a South African gold mine, their presence tells us not to be too doctrinaire about what we consider a habitable environment.

The Wall Street Journal‘s fine science correspondent Sharon Begley goes still further in her latest entry:

Something else improves the odds that we are not alone: the building blocks of life are nearly as common in interstellar space as beer at ballparks. In August, astronomers announced they had found eight new biologically significant molecules deep in the giant clouds of gas and dust that spawn planets.

Although names like “methyl-cyano-diacetylene” might not evoke visions of whales or roses or other living things, these carbon-based molecules are the precursors to life. The new octet brings to 141 the number of different organic molecules found in interstellar space, all of which fall onto the surface of planets like seeds.

A universe seeded with life sounded preposterous not so long ago. Now the notion is gaining plausibility. It may take, as Gregory Benford reminds us, human feet on the ground on the Red Planet to conclusively make the call for Mars, but when and if we do find life there, the odds on other abodes in our own Solar System — and certainly around other stars — go up as well.

Comments on this entry are closed.

  • Adam October 28, 2006, 19:22

    There’s an article in this week’s “New Scientist” which suggests a definitive test – feeding a soil sample with organics of both chiralities and comparing the ‘exhalation’ response. Chemistry would decompose both types equally, while biology would show a preference for one over the other. They reckon the experiment can be made the size of a milk carton and multiple mini-labs could be deployed around a lander to avoid biasing by different soil types.

    I got all excited by Gil Levin’s colour-change paper years ago – he reported greening of the rocks in Viking photos in line with seasonal changes – but Mars-is-Mars and may not be as simple as we imagine. For example UV might not make enough super-oxides to explain organic decomposition in the soils tested by Viking, but the electric fields of the dust very well might – something we’ve only learnt recently. Mars isn’t Earth, even if we find a few good analogues here in the Atacama and Antarctica.


  • Administrator October 28, 2006, 19:54

    The article Adam mentions is here:


    And at last look, it’s still outside the New Scientist firewall.

    Adam, I second your thoughts on the color-change issue — very interesting, but as you say, we have much to learn about this alien environment.

  • Adam October 29, 2006, 19:03

    Just another thought. I’ve mentioned Charles Lineweaver’s thermobiology paper already, but he also famously worked out the peak period of Earth-like planet formation in our Galaxy as about 1.9 billion years ago. If “plasma panspermia” is true – that bacteria have been launched off into deep space by detached plasmoids from Earth’s magnetotail – then it’s likely to have begun elsewhere in our Galaxy much earlier and spread here.

    So I wonder how similar life will be through-out the Galaxy. Certainly not naively parallel like in “Star Trek” where most humanoid species are panspermia descendents of an ancestral species from aeons ago that deliberately seeded millions of worlds. Possible, but unlikely and unnecessary if bacteria (or their precursors) can spread naturally. The odds are against random convergence of gene lineages across such a time-scale – which is an important piece of evidence for common descent of all terrestrial life.

    And will life have adapted to new environments by adopting new amino acids and novel genetic codings? There are a few species that use variations on the standard codon sequences and 20 amino acids, and molecular biologists believe they can incorporate a lot more divergent possibilities. The basic DNA-RNA format might have a lot more surprises left in it than what our biosphere has explored. It will certainly need them to have adapted to, say, ammonia/water mixtures on icy moons.


  • Joseph Baneth Allen October 30, 2006, 12:16

    One way to test if the reported greening of the rocks in Viking photos is due seasonal changes from life or chemical reactions is to see if one or both of the landers can be reactivated and compare new photos of the rocks to old photos.

    On a sidebar – one, almost odd fact about the Viking Landers, is that while Carl Sagan tested the cameras in the desert to see if they could detect the types tracks made by animals. To the best of my knowledge, nobody has tested the cameras on Spirit and Opportunity to see if they could visually identify fossils and or current life forms.

  • ljk January 8, 2007, 0:46


    Viking Mission Results Indicates Presence of Life on Mars

    2007-01-07 16:15:18

    We may already have ‘met’ Martian organisms, according to a paper presented Sunday (Jan. 7) at the meeting of the American Astronomical Society in Seattle.

    Dirk Schulze-Makuch of Washington State University and Joop Houtkooper of Justus-Liebig-University, Giessen, Germany, argue that even as new missions to Mars seek evidence that the planet might once have supported life, we already have data showing that life exists there now—data from experiments done by the Viking Mars landers in the late 1970s.

    “I think the Viking results have been a little bit neglected in the last 10 years or more,” said Schulze-Makuch. “But actually, we got a lot of data there.” He said recent findings about Earth organisms that live in extreme environments and improvements in our understanding of conditions on Mars give astrobiologists new ways of looking at the 30-year-old data.

    The researchers hypothesize that Mars is home to microbe-like organisms that use a mixture of water and hydrogen peroxide as their internal fluid. Such a mixture would provide at least three clear benefits to organisms in the cold, dry Martian environment, said Schulze-Makuch. Its freezing point is as low as -56.5o C (depending on the concentration of H2O2); below that temperature it becomes firm but does not form cell-destroying crystals, as water ice does; and H2O2 is hygroscopic, which means it attracts water vapor from the atmosphere—a valuable trait on a planet where liquid water is rare.

    Schulze-Makuch said that despite hydrogen peroxide’s reputation as a powerful disinfectant, the fluid is also compatible with biological processes if it is accompanied by stabilizing compounds that protect cells from its harmful effects. It performs useful functions inside cells of many terrestrial organisms, including mammals. Some soil microbes tolerate high levels of H2O2 in their surroundings, and the species Acetobacter peroxidans uses hydrogen peroxide in its metabolism.

    Possibly the most vivid use of hydrogen peroxide by an Earth organism is performed by the bombardier beetle (Brachinus), which produces a solution of 25 percent hydrogen peroxide in water as a defensive spray. The noxious liquid shoots from a special chamber at the beetle’s rear end when the beetle is threatened.

    He said scientists working on the Viking projects weren’t looking for organisms that rely on hydrogen peroxide, because at the time nobody was aware that such organisms could exist. The study of extremophiles, organisms that thrive in conditions of extreme temperatures or chemical environments, has just taken off since the 90s, well after the Viking experiments were conducted.

    The researchers argue that hydrogen peroxide-containing organisms could have produced almost all of the results observed in the Viking experiments.

    • Hydrogen peroxide is a powerful oxidant. When released from dying cells, it would sharply lower the amount of organic material in their surroundings. This would help explain why Viking’s gas chromatograph-mass spectrometer detected no organic compounds on the surface of Mars. This result has also been questioned recently by Rafael Navarro-Gonzalez of the University of Mexico, who reported that similar instruments and methodology are unable to detect organic compounds in places on Earth, such as Antarctic dry valleys, where we know soil microorganisms exist. • The Labeled Release experiment, in which samples of Martian soil (and putative soil organisms) were exposed to water and a nutrient source including radiolabeled carbon, showed rapid production of radiolabeled CO2 which then leveled off. Schulze-Makuch said the initial increase could have been due to metabolism by hydrogen peroxide-containing organisms, and the leveling off could have been due to the organisms dying from exposure to the experimental conditions. He said that point has been argued for years by Gilbert Levin, who was a primary investigator on the original Viking team. The new hypothesis explains why the experimental conditions would have been fatal: microbes using a water-hydrogen peroxide mixture would either “drown” or burst due to water absorption, if suddenly exposed to liquid water. • The possibility that the tests killed the organisms they were looking for is also consistent with the results of the Pyrolytic Release experiment, in which radiolabeled CO2 was converted to organic compounds by samples of Martian soil. Of the seven tests done, three showed significant production of organic substances and one showed much higher production. The variation could simply be due to patchy distribution of microbes, said Schulze-Makuch. Perhaps most interesting was that the sample with the lowest production—lower even than the control—had been treated with liquid water.

    The researchers acknowledge that their hypothesis requires further exploration. “We can be absolutely wrong, and there might not be organisms like that at all,” said Schulze-Makuch. “But it’s a consistent explanation that would explain the Viking results.”

    He said the Phoenix mission to Mars, which is scheduled for launch in August, 2007, offers a good chance to further explore their hypothesis. Although the mission’s experiments were not designed with peroxide -containing organisms in mind, Phoenix will land in a sub-polar area, whose low temperatures and relatively high atmospheric water vapor (from the nearby polar ice caps) should provide better growing conditions for such microbes than the more “tropical” region visited by Viking. Schulze-Makuch said the tests planned for the mission, including the use of two microscopes to examine samples at high magnification, could reveal whether we had the answer all along—and if we’ve already introduced ourselves to our Martian neighbors in a harsher way than we intended.

    “If the hypothesis is true, it would mean that we killed the Martian microbes during our first extraterrestrial contact, by drowning—due to ignorance,” said Schulze-Makuch.

  • ljk May 20, 2008, 8:45

    The Fall and Rise (and Fall?) of Life on Mars (pdf)

    After decades of searching, no one’s found life on Mars —
    or have they? More…


  • ljk April 11, 2009, 8:11

    Mars Before the Space Age

    Authors: Barrie W Jones

    (Submitted on 17 Nov 2008 (v1), last revised 14 Jan 2009 (this version, v3))

    Abstract: Mars has surely been scrutinised since the dawn of humankind. In the 16th century Tycho Brahe made accurate observations of the position of Mars that enabled Johannes Kepler to obtain his first two laws of planetary motion. In the 17th century the first telescope observations were made, but very little surface detail could be discerned. Throughout the 18th and 19th centuries telescopes improved, revealing many dark areas on the red tinted surface.

    After the close opposition of 1877 Giovanni Schiaparelli announced about 40 canali on Mars. This led to the saga of the canals of Mars, laid to rest in 1971 when Mariner 9 made observations from Martian orbit showing that the canali/canals of Mars do not exist.

    Belief that there was life on Mars was widespread in the 19th century, including the view that the dark areas were some form of plant life. This view persisted until Mariner 4 flew past Mars in 1965 and discovered a far thinner atmosphere than previously thought, with impact craters dominating the images.

    It was Mariner 9 that revealed much more promising landscapes. Thus, the contemporary era of Mars exploration began. Our picture of Mars today is not only much more complete that that before Mariner 4, in several ways it is quite different.

    The belief however, that there may be life on Mars persists – subsurface life cannot be ruled out and, failing that, there might be ancient fossils on Mars.

    Comments: 13 pages as published, 13 Figures

    Subjects: Astrophysics (astro-ph); Popular Physics (physics.pop-ph); Space Physics (physics.space-ph)

    Journal reference: Int. J. Astrobiol. vol. 7 no. 2, 143-155 (2008)

    Cite as: arXiv:0811.2700v3 [astro-ph]

    Submission history From: Barrie W. Jones [view email]

    [v1] Mon, 17 Nov 2008 13:19:44 GMT (553kb)

    [v2] Tue, 13 Jan 2009 10:56:44 GMT (2228kb)

    [v3] Wed, 14 Jan 2009 11:28:15 GMT (553kb)