Experiments prompted by a 2008 "surprise" from NASA's Phoenix Mars Lander suggest that soil examined by NASA's Viking Mars landers in 1976 may have contained carbon-based chemical building blocks of life.
"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, Moffett Field, Calif. according to a statement by NASA on Sept. 3.
McKay is one of the authors of a study published online by the Journal of Geophysical Research under the title "Planets, reanalyzing results of Viking's tests for organic chemicals in Martian soil".
The only organic chemicals that were identified when the Viking landers heated samples of Martian soil, were chloromethane and dichloromethane. These are chlorine compounds interpreted at the time as likely contaminants from cleaning fluids.
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 same manner that the Viking tests had been done.
"We were looking at a jigsaw puzzle with a piece missing"
"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, which is 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.
"Our results suggest that not only organics, but also perchlorate, may have been present in the soil at both Viking landing sites," added Rafael Navarro-González, the study's lead author.
The NASA statement points out 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."
Upcoming missions to Mars and further work on meteorites from Mars are expected to study this in more detail:
The Curiosity Rover that NASA's Mars Science Laboratory mission will deliver to Mars in 2012 will carry the Sample Analysis at Mars (SAM) instrument. In contrast to Viking and Phoenix, Curiosity can rove and thus analyze a wider variety of rocks and samples.
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.