Life on Mars?
Posted: Wednesday, August 02, 2006 5:25 PM by Alan Boyle
Static buildup may explain a three-decade-old mystery in the search for life on the Red Planet. Researchers say the static electricity generated by Martian dust storms could provide an alternate explanation for chemical reactions that hinted at organic activity – reactions that were detected during the 1976 Viking mission. Their findings also imply that the Martian surface would be continually sterilized by hydrogen peroxide.
All that is bad news for astrobiologists looking for signs of Martian life, but there's a flip side as well: The researchers acknowledge that organisms could still lurk far below the surface. And one of them says the new findings raise deeper questions about the recent detection of methane in Mars' atmosphere, which may (or may not) be an indicator of microbial life.
The Viking mission stirred up a long-simmering controversy because one of the experiments - which involved adding water and nutrients to Martian soil, then cooking the brew - briefly produced the kinds of gases that might be expected to result from organic activity. Those results could not be confirmed, however, leading researchers to wonder whether non-biological chemistry could have explained the reaction.
The prime suspect was hydrogen peroxide. If peroxide accumulated in the Martian soil, that might explain the reaction - but where could all that peroxide come from?
NASA |
Artwork shows a Martian dust storm with electrical
charges labeled as positive and negative.
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In a pair of studies published in the June issue of Astrobiology, researchers say the dust devils and dust storms that sweep over the Red Planet could generate enough static electricity to split carbon dioxide and water molecules in the atmosphere. Those molecules could recombine as hydrogen peroxide and other oxidizing agents that would fall out of the air like snow - and sterilize the surface.
"We actually see some analogs on the earth," the University of Michigan's Sushil Atreya, one of the lead authors of the research, told me Monday. "In terrestrial dust devils, for example, the electric fields are quite large, and there is chemical modification that goes on in the dust devils."
Another lead author, Gregory Delory of the University of California at Berkeley, said in a news release that such a scenario "very much affects the interpretation of soil measurements made by the Viking landers in the 1970s." The chemical reactions proposed by the researchers would produce enough peroxide to explain the results of the controversial Viking experiment without organic activity, the researchers said.
If oxidizing snow is indeed falling on Martian soil, that would add just one more factor inimical to any organisms that are even thinking about going topside on Mars. There are plenty of other reasons why life as we know it would have a hard time on the present-day planet - including deadly ultraviolet radiation, low temperatures and the lack of water.
The findings have implications for future exploration as well. "It is possible there could be long-term corrosive effects that would impact crews and equipment due to oxidants in the Martian soil and dust," Delory said.
As for the search for Martian life, Delory said "the jury is still out." Organisms may have arisen on Mars billions of years ago, when the planet was warmer and wetter, and some form of life may well still exist. But if it's "life as we know it," those organisms would have to be sheltered below the surface, Atreya said.
Mars' deep subsurface has long been considered the most likely place to look for extraterrestrial life, because that's where liquid water may persist - perhaps 1 to 6 miles (2 to 10 kilometers) deep, Atreya said. "I don't believe the peroxide is going to penetrate that far down below the surface," he observed.
Atreya noted that the peroxide proposal would raise questions about the methane detected in Mars' atmosphere. If the latest hypothesis pans out, then chemical reactions on Mars would have to produce even more methane than previously thought.
On Earth, the prime method for methane production is biological activity - which is why the methane in Mars' atmosphere is so interesting to astrobiologists. But Atreya pointed out that there are other ways to make methane. For example, the gas could be "produced geologically in the interior, not by a volcanic process, but by some sort of hydrothermal process conducted at low temperatures," Atreya said.
It will take further experiments on Mars itself to resolve these questions. One experiment slated for inclusion on the Mars Science Laboratory, due for launch in 2009, would measure the proportions of carbon isotopes - which could be an indicator for the presence or absence of biological activity. The mission's scientific instruments would also check for oxidants, which could provide evidence for or against the peroxide proposal, Atreya said.
"Unfortunately we have to be a little bit patient, but it's not that far away," he told me.
In addition to Delory and Atreya, the team members behind the Astrobiology studies include William Farrell of NASA's Goddard Space Flight Center, Nilton Renno and Ah-San Wong of the University of Michigan, Steven Cummer of Duke University, Davis Sentman of the University of Alaska, John Marshall of the SETI Institute, Scot Rafkin of the Southwest Research Institute and David Catling of the University of Washington. The research was funded by NASA.
This year marks a couple of big anniversaries in NASA's search for Martian life, including the 30th anniversary of the Viking landings as well as the 10th anniversary of the announcement that "nanofossils" had been found within a Mars meteorite. Check out this time line for a chronology of the quest, scan this 1998 interview with one of the researchers behind the Mars meteorite claims, watch this video, and stay tuned for more in the next few days.
Update for 5:25 p.m. ET Aug. 2: One of the key proponents of a biological explanation for the Viking experiment's results is Gilbert Levin, who was the principal investigator for the Labeled Release experiment, also known as the LR. Levin told me today that the peroxide proposal has been around for about 29 years, and he's definitely not convinced by the latest research.
"Thirty years is time enough for someone to have made a case against the LR. and I point out that no scientific case has ever been made," Levin said.
Until recently, remote observations had not turned up evidence of significant amounts of hydrogen peroxide in the Martian atmosphere. However, two years ago, researchers using the James Clerk Maxwell Telescope in Hawaii said they had detected levels of peroxide that were consistent with theoretical predictions. Similar reports came from the Paris Observatory.
Even if there is peroxide present, Levin said chemical activity alone wouldn't explain the results from his experiment. He noted that the reactions took place under warm and wet conditions, but did not occur once the samples were warmed to a high temperature, then cooled. Levin saw that as a sign that whatever was causing the reaction at lower temperatures was killed off by the higher temperatures.
"What I want somebody to do is to duplicate those results chemically," Levin told me. "I can duplicate them biologically all the time."
For details, check out Levin's file of research on the Labeled Release experiment.
All the research aimed at ruling out life on Mars must make Levin feel like a voice crying out in the wilderness - but he'll get his say Aug. 14 at an International Society for Optical Engineering conference in San Diego. He's due to present a paper titled "Modern Myths of Mars," and is a co-chair for several provocative sessions on the search for Red Planet life. Who knows? Gilbert Levin may have the last word after all.
