Trace of gas not enough to be sign of life
JPL-Caltech/NASA and MSSS
After months of searching, the NASA rover Curiosity detected no appreciable methane in Mars’ atmosphere, disappointing scientists who had hoped to find a strong sign of life on the Red Planet.
On Earth, microbes have churned out as much as 95 percent of all atmospheric methane, so finding that gas in Mars’ air would have been solid circumstantial evidence of life. Instead, the rover measured no more than a trace of methane, with an average concentration of a mere 0.18 parts per billion (SN: 10/19/13, p. 7).