Life on Mars? Maybe We Missed It
Oct. 24, 2006 — -- Thirty years ago, the first robot probes from Earth landed on Mars, scooped up soil, and generated a wave of excitement -- which quickly died.
The Viking landers carried miniature laboratories. They fried Martian soil samples to see if there were telltale signs of life in the vapor that was created. The first results were tantalizing, but soon the consensus was that Viking had found nothing.
Or so it seemed. Now a team of Mexican scientists has gone back and re-examined the Viking experiment. Their conclusion: no saying yet whether there's life on Mars -- but if there is, we probably missed it.
Is There Life on Mars? How About Life on Earth?
Viking's experiment "may be blind to low levels of organics on Mars," write Rafael Navarro-Gonzalez and several fellow researchers in this week's edition of "Proceedings of the National Academy of Sciences."
To prove their point, the scientists repeated the test on soil from some of the most desolate places on earth -- the Dry Valleys of Antarctica, and the deserts of Chile and Libya.
The remarkable thing about such places is that despite blazing sun, frigid nights, and little moisture, they are home to living things. When a few minimal conditions are met on earth -- light or other energy, and at least a little bit of liquid water -- life thrives.
Not according to the Viking experiment. If Martians had sent it on a probe to land in Libya, it would have reported no life here.
For the record, the experiment in question was called "TV-GC-MS" -- short for Thermal Volatization-Gas Chromatography-Mass Spectrometry. It literally vaporized Martian soil samples, then examined the gases that resulted to see if there were telltale signs of organic molecules.
Another experiment looked for signs of slightly radioactive carbon, which would be another sign of life. It found there were a lot of chemical reactions going on in the soil Viking scooped up with its robot arm. But for lack of results from the TV-GC-MS experiment, most scientists concluded Viking had some up dry.
Cautious Ever Since
The results were sobering enough that NASA did not try to send another probe to Mars until 1993. And in its efforts since, it's been careful to say it is not actually looking for life, just signs that Mars might once have been a good place for life.
"The new logic," wrote NASA's Christopher McKay in an email to ABC News, "is: 1) water, 2) organics, 3) signs of life. We are just about to move from step 1 to step 2. This is why this paper is relevant to upcoming missions."
McKay, one of NASA's lead scientists in Mars exploration, was also senior author of this week's paper. He oversaw the research, and approved it before it was published for other scientists to read.
"We believe the pathway to finding life is to follow the water," said Firouz Naderi, who was manager of NASA's Mars exploration program when the two Mars Exploration Rovers, Spirit and Opportunity, landed there in 2004.
The rovers, which are both still going, have succeeded; scientists say their pictures and readings show ample signs that there was once moisture in the Martian soil. But life? If there were microbes in the rovers' tread marks, the two probes would not have a direct way to test them.
NASA will get more ambitious with a its next two probes, scheduled to land on Mars in 2008 and 2010. They will carry updated versions of Viking's experiments, looking for evidence of organic materials in Martian soil samples.
So the Viking story, say the authors of this week's study, is a cautionary one. "It is important," they write, "that future missions to Mars include other analytical methods to search for extinct and/or extant live in the martian soil."