As scientists search for clues of past life on Mars, the presence of methane has been particularly sought after.
According to Astrobiology Magazine, Curiosity team members detailed a methane burst in Dec. 2014, but waited a year to publish a study on their discovery. The Mariner 7 spacecraft first detected methane gas on Mars' south pole some 50 years ago and the search has been ongoing since.
Curiosity collected six atmospheric samples between Oct. 2012 and June 2013, but mission managers found no evidence of methane. Shortly after, the rover detected four methane bursts in two months.
Spacecraft had detected similar methane bursts in 2003 and 2004, appearing and vanishing relatively quickly.
"We are continuously monitoring that methane amount, and there hasn't been evidence of any leakage during the entire mission," Chris Webster, a senior research scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif., told Astrobiology. "And while it's true that the concentration of methane in that chamber is 1,000 times higher than in Mars' atmosphere, the comparison is actually misleading."
Curiosity may have spiked its own methane reading on Mars with some gas it collected before taking off from the Cape Canaveral Air Force Base. Webster, lead author on the Dec. 2014 study, told the magazine there are plenty more factors to consider.
"You have to look at the amount of methane, not the concentration," he said. "The concentration of methane on the rover may seem high, but the actual amount is very small because the chamber is very small. To produce the amount we detected in Mars' atmosphere, you'd need a gas bottle of pure methane leaking from the rover. And we simply don't have it."
Kevin Zahnle, a scientist at NASA's Ames Researcher Center in Moffett Field not involved in the recent study, was critical of both the 2003-2004 and the 2013-2014 discoveries.
"I am convinced that they really are seeing methane," he told Astrobiology. "But I'm thinking that it has to be coming from the rover."
