The US space agency's (Nasa) Curiosity rover has detected the intermittent "belching" of methane gas on Mars.
The robot sees very low-level amounts constantly in the background, but it also has monitored a number of short-lived spikes that are 10 times higher.
Methane on the Red Planet is intriguing because here on Earth, 95% of the gas comes from microbial organisms.
Researchers have hung on to the hope that the molecule's signature at Mars might also indicate a life presence.
The Curiosity team cannot identify the source of its methane, but the leading candidate is underground stores that are periodically disturbed.
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BBC News - Methane 'belches' detected on Mars