Scientists expressed their disappointment on Thursday when Nasa's Mars Curiosity rover was unable to detect methane in the planet's atmosphere, a gas that on Earth is a strong indicator of life.
The finding does not bode well for the possibility that microbes capable of producing the gas could be living below the planet's surface, where conditions would be less harsh.
Earth based telescopes and satellites had observed "plumes" of methane gas in the martian atmosphere for the last decade. "Small but significant" volumes of methane were observed from Mars orbit showing localised patches.
Curiosity rover had been sent to the planet in the hope of detecting signs of the gas, which is considered a potential signifier of current or past biological activity.
But Curiosity's failure to identify any signs of the gas may now dent the optimistic belief held by scientists that life could exist on Mars. Although it lacks the technology to directly search for life, the car-sized rover breathed in Mars air and scanned it to look for signs of methane.
On Earth, most of the gas is a byproduct of life, released when animals digest or plants decay.
“Every time we looked, we never saw it,” said Christopher Webster, of NASA's Jet Propulsion Laboratory, who led the research published online in the journal Science.
Webster said while the result was “disappointing in many ways,” the hunt for the elusive gas continues. While methane is linked to living things, it can also be made by non-biological processes.
The results reduce "the probability of current methanogenic microbial activity on Mars, and limits the recent contribution from extraplanetary and geologic sources," the authors summarised.
Michael Mumma of NASA's Goddard Space Flight Center previously noticed a mysterious burst of methane from three regions in Mars' western hemisphere. Despite the findings, Mumma, who had no role in the latest study, has said he stood by his observations.
Earlier this month, Curiosity reached its first rest stop in its long trek toward Mount Sharp, a mountain rising from Gale Crater near the equator. The rover will take monthly readings of the Martian atmosphere during the road trip, expected to last almost a year.
The rover previously found evidence of an ancient environment that could have once been suitable for microscopic life. Scientists still hope to uncover signs of organic molecules, considered the chemical building blocks of life, at the base of Mount Sharp.