In a news release Thursday, NASA says the results were unexpected because of the previous detection of methane in the atmosphere of Mars by other probes and telescopes.
The new findings reduce the probability of finding living, methane-making bacteria below the surface of Mars, says a new study published Thursday online in the journal Science Express.
The study, led by Christopher Webster, of the California Institute of Technology Jet Propulsion Laboratory, also calls into question controversial measurements of large amounts of methane by satellites orbiting Mars and “plumes” of methane in the Martian atmosphere measured by NASA scientists with a telescope from Earth in 2003. The estimated 19,000 tonnes of methane had nearly disappeared by 2006, leaving scientists stumped about how that happened.
“There currently remains no accepted explanation for the existence and distribution of the reported plumes, nor of the apparent disappearance of methane over the last few years,” wrote Webster and his team.
The new results are based on data collected on six occasions between October 2012 and June 2013 using a tunable laser spectrometer, an instrument on the Curiosity rover specially designed for measuring methane on Mars.
Average methane concentrations in the Mars atmosphere were found to be 0.18 parts per billion by volume – essentially, zero. The researchers calculated that that means the maximum possible amount of methane in the Martian atmosphere today is 1.3 parts per billion – about six times lower than measurements taken by by a variety of orbiters and telescopes in the past decade or so.
Scientists had been very interested in finding methane on Mars as a possible indication of life. On Earth, 90 to 95 per cent of the methane in the atmosphere has been produced by living organisms, both those alive today and those that lived millions of years ago, decomposing into fossil fuels such as methane.
Michael Meyer, NASA’s lead scientist for Mars exploration, said the “important” new result would “help direct efforts to examine the possibility of life on Mars.”
He said the finding didn’t rule out the existence of microbial life on Mars, since many microbes on Earth don’t generate methane.
The new study also suggests there is likely very little methane on Mars even from non-biological sources, such as comets or interplanetary dust.