On Mars, NASA Curiosity rover finds largest amount of methane ever measured during its mission

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NASA's Curiosity Mars rover has found the largest amount of methane ever measured during its mission on the Red Planet -- about 21 parts per billion units by volume (ppbv), the US space agency said.

One ppbv means that if you take a volume of air on Mars, one billionth of the volume of air is methane, according to the US space agency.

The finding came from the rover's Sample Analysis at Mars (SAM) tunable laser spectrometer.

It is exciting because microbial life is an important source of methane on Earth, but methane can also be created through interactions between rocks and water, NASA said in a statement.

Curiosity does not have instruments that can definitively say what the source of the methane is, or even if it is coming from a local source within Gale Crater or elsewhere on the planet.

"With our current measurements, we have no way of telling if the methane source is biology or geology, or even ancient or modern," said SAM Principal Investigator Paul Mahaffy of NASA's Goddard Spaceflight Center in the US.

The Curiosity team has detected methane many times over the course of the mission.

Previous papers have documented how background levels of the gas seem to rise and fall seasonally.

They have also noted sudden spikes of methane, but the science team knows very little about how long these transient plumes last or why they are different from the seasonal patterns.

The SAM team has organised a different experiment to gather more information on what might be a transient plume.

Whatever they find -- even if it is an absence of methane -- will add context to the recent measurement, NASA said.

Curiosity's scientists need time to analyse these clues and conduct many more methane observations.

They also need time to collaborate with other science teams, including those with the European Space Agency's Trace Gas Orbiter, which has been in its science orbit for a little over a year.

Combining observations from the surface and from orbit could help scientists locate sources of the gas on the planet and understand how long it lasts in the Martian atmosphere.

That might explain why the Trace Gas Orbiter's and Curiosity's methane observations have been so different, according to NASA.