Nasa's Curiosity rover has measured the Red Planet's atmospheric composition.
The robot sucked the air into its big Sample Analysis at Mars (Sam) instrument to reveal the concentration of different gases.
It is the first time that the chemistry of the atmosphere has been tested from the surface of the planet since the Viking landers in the 1970s.
The Sam analysis is ongoing but no major surprises are expected at this stage - carbon dioxide will dominate.
CO2 is the chief component of the Martian air, as the Viking probes found. Of keener interest will be whether a signal for methane has been detected by Curiosity.
The gas has recently been observed by satellite and by Earth telescopes, and its presence on the Red Planet is intriguing.
Methane should be short-lived and its persistence suggests a replenishing source of some kind - either biological or geochemical. It is hoped Sam can shed light on the issue.
The results from this first test could be announced next week, said Curiosity deputy principal scientist Joy Crisp, but she cautioned that it would be some time before definitive statements could be made about the status of methane on Mars ( via bbc.co.uk ).