Los Angeles - Nasa's Curiosity rover has sniffed Martian air and there's no sign of methane.
That's the conclusion from a new study released on Thursday in the journal Science. On Earth, the gas is linked to living things, released when animals digest.
Scientists say the lack of methane in Curiosity's experiments does not bode well for the search for microbial life underground.
Curiosity landed in Gale Crater near the Martian equator last year. For the first eight months, it used a tiny laser to sample the air, but came up empty-handed in the search for methane.
This contradicts previous observations from orbiting spacecraft and Earth-based telescopes that found plumes of methane on Mars.
Curiosity is headed toward a mountain and will continue to hunt for methane during the long drive.