Martian soil could contain the building blocks of carbon-based life after all, a new study suggests, despite the negative results of an analysis performed by the Viking missions 34 years ago.

When two Viking landers visited Mars in 1976 and scooped up soil samples, scientists were surprised that the craft failed to unearth evidence of organic compounds. The apparent lack of organic molecules helped cement the notion that Mars would not easily support life.

But a new study, relying on soil samples from Earth, now suggests that the Viking craft may have found organic compounds from Mars but failed to recognize them. The finding represents a sea change in the way many scientists think about Mars and suggests a specific strategy for searching for vestiges of life on the planet, says study coauthor Rafael Navarro-Gonzalez of the National Autonomous University of Mexico in Mexico City.

Navarro-Gonzalez and collaborators, including astrobiologist Chris McKay of NASA's Ames Research Center in Moffett Field, Calif., describe their work in an upcoming Journal of Geophysical Research-Planets. They also reported the findings September 6 in a press briefing at the National Autonomous University.

The study was inspired by a soil analysis conducted by the Mars Phoenix Lander, which arrived on Mars in 2008. Phoenix found that most of the chlorine at the landing site was in the form of perchlorate, rather than a chloride salt as had been assumed (SN.. 4/11/09, p. 12).

When heated, perchlorate breaks down into fragments that destroy organic compounds. …