Did NASA kill alien lifeforms thirty years ago? Maybe. According to two astrobiologists, NASA's Viking landers, which touched down on Mars in 1976 to search for life on the Red Planet, may actually have destroyed Martian micro-organisms in the process.
The Viking experiments were designed to look for Earth-like life on the Mars. Samples of Martian soil, scooped up by the spacecraft's robotic arm, were exposed to a variety of in-situ tests. In one experiment, nutrient-rich water was added to the sample to see if any organisms that might be present would feed themselves. Another experiment cooked the sample to see if any organic residue would be left.
But according to geologists Dirk Schulze-Makuch of Washington State University in Seattle and Joop Houtkooper of the Justus Liebig University in Giessen, Germany, Martian micro-organisms may be radically different from Earthly water-based life-forms. In particular, the fluid in their cells may not be water, but a mixture of water and hydrogen peroxide. That may explain the origin of a highly oxidizing chemical substance on the Martian surface, thought to be hydrogen peroxide. According to Schulze-Makuch and Houtkooper, the aggressive stuff might have a biological origin.
If such organisms exist on Mars, they would not have survived the Viking nutrient experiment, the researchers report. Instead, they would have been literally drowned to death, because they wouldn't be able to cope with large quantities of water. Also, the cooking experiment would not leave organic residue, because organic molecules would be destroyed by the released hydrogen peroxide.
Schulze-Makuch's presentation here at the 209th meeting of the American Astronomical Society drew a lot of media attention, but it was greeted with cautious skepticism by other scientists. "It's a pretty neat idea," says Michael A'Hearn, an astronomer at the University of Maryland, College Park. But even though it looks like the Viking experiments could indeed have killed hydrogen peroxide-based organisms, that doesn't necessarily mean life exists on Mars, he says. Astrobiologist John Baross of the University of Washington in Seattle agrees that it is certainly conceivable that the Viking experiments failed to detect alien micro-organisms. Still, he says, "I can't imagine any carbon-based life form that could survive close to the Martian surface, given the high levels of lethal radiation."