The six-wheeled NASA Mars rover in June detected methane levels approximately 21 parts per billion per unit volume (ppbv) inside the 96-mile-wide (154km) Gale Crater. This was far higher than the expected background concentration at Gale, which NASA has calculated ranges seasonally from 0.24 ppbv to 0.65 ppbv.
The result made headlines around the world as methane is associated with life on Earth.
However, the view from above mysteriously paints a very different picture.
The European-Russian Trace Gas Orbiter (TGO), specifically built two detect such low-abundance gases has found the air on Mars to be virtually methane-free.
TGO for example recorded an upper limit of 0.012 parts per billion (ppb) methane during its first four months of full science operations.
However, this is not the only possible explanation for the inconsistency.
Dr Ashwin Vasavada he told Space.com: “Maybe the expansion and contraction of the atmosphere every day from solar heating is responsible.”
The Curiosity Rover’s previous methane measurements, made using its Sample Analysis at Mars (SAM) instrument were collected at night.
The Curiosity Rover has consequently only hunted for methane when the Martian atmosphere was relatively dense and, meaning the methane was more concentrated.
The Red Planet’s atmosphere expands during the Martian day, the methane becomes more mixed and spread out, which may explain why the orbiters’ observations are so different.
This idea is now being put to the test by NASA, with the rover scheduled to make its first-ever detailed daytime methane measurement last week.
Dr Catherine O’Connell, a planetary geologist at the University of New Brunswick, said: “This rare experiment is a chance to get some exciting science observations, but we’ll need time after the experiment to analyse the data; we don’t expect to have any takeaways right away.”
Methane can also be created abiotically as well, most commonly by reactions between hot water and rock.
And even if the Mars methane is biological cause, it is not a guarantee of active alien life.
Methane may have been generated billions of years ago in underground pockets.
And this gas may only now be slowly seeping out of the Red Planet’s rock.