While not necessarily evidence of life itself, these findings are a good sign for future missions exploring the planet's surface and subsurface.
"I don't believe there's life on Mars at the present", Freeman says, because Mars is very dry, very cold and lacks much of an atmosphere. This is also when life was evolving on our own planet. What's not yet clear is whether or not the methane is, indeed, biological. It arrived at Mars in 2016 and is now mapping concentrations of methane and other gases from on high.
The sediments, analysed by the SAM instrument on Curiosity, come from just below the surface, where they have been shielded from most of the UV radiation that would break down organic molecules exposed on the surface.
The Gale Crater was once filled with water fed by streams.
Mars's Gale Crater, where Curiosity has been trolling around for the past six years, is a particularly interesting place to look for those molecules. Over time, a picture of the ebb and flow of methane on Mars has emerged. The Wikipedia article on "organic matter" makes the point: "Organic molecules can also be made by chemical reactions that don't involve life". "We thought Mars was dead internally", Harrison said.
"The only thing that fits the data is that you have a source of methane below the surface".
"We can not rule out its creation from biological activity ..."
"With this new data, we again can not rule out microbial activity as a potential source", Webster said.
"As temperatures change from winter to summer, the methane changes greatly because as the surface gets a little bit warmer it releases a lot more methane", he said.
The Curiosity rover has not been able to find the source of the organic molecules in its findings, according to the report. Sadly, most scientists dismissed this claim in the decade that followed - finding other explanations for the rock's formation.
Jen Eigenbrode, of NASA's Goddard Space Flight Center, said these findings "bode well" in the space agency's attempts to unlock the Red Planet's past and formation. The key samples in the latest findings came from a spot 6.4 kilometres away.
Curiosity dug up samples at Mojave and Confidence Hills near Pahrump Hills. Now Curiosity shows that these carbon-based compounds do indeed exist. The term "organic" is ambiguous - we often take it to mean "life-related" but it doesn't have to mean that.
The methane could simply be the product of basic geological processes, but it's possible the gas has origins in biological sources.
A seasonal change in methane levels is exciting, he said, because 95 percent of the methane observed on Earth is the result of biology. The event would be aired live on NASA Television. And, of course, there is always the chance that Martian methanogens still slumber in the planet's subsurface even today, periodically awakening during clement periods to produce their gaseous calling-card.
While the Curiosity Rover only scrapes off the top 5 centimetres, ExoMars's MOMA lab which is planned to be launched in 2020 will go down 2 metres.
Webster theorizes the methane created either now or long ago is seeping from deep underground reservoirs up through cracks and fissures in the crust.
NASA's Curiosity Mars Rover snaps a self-portrait at a site called Vera Rubin Ridge on the Martian surface in February 2018 in this image obtained on June 7, 2018.