Researchers at the space agency announced Thursday that the Curiosity rover has discovered strong concentrations of organic molecules in 3-billion-year-old sedimentary rocks on the red planet's surface.
Finding methane in the atmosphere and ancient carbon preserved on the surface gives scientists confidence that NASA's Mars 2020 rover and ESA's (European Space Agency's) ExoMars rover will find even more organics, both on the surface and in the shallow subsurface.
What the study has done, though, is to propel the search for life on Mars higher up the list of worldwide space exploration priorities - giving space agencies ammunition to argue for a coordinated programme of missions to explore the Red Planet.
The methane could simply be the product of basic geological processes, but it's possible the gas has origins in biological sources.
NASA's Curiosity Rover has explored the surface of Mars for five years, and has recently resumed drilling into rocks on the surface.
That doesn't mean they've found life, but it's a good indication Mars could have sustained life in the past.
"If there are no organics, we can pretty much forget about there being life or ever having been life on Mars", says Dr. Weintraub.
The methane observations provide "one of the most compelling" cases for present-day life, she said.
The most exciting news is that the changes definitely match the Martian seasons, hitting a peak at the end of summer in the northern hemisphere.
"Not only have we got this wonderful repeatability, but the seasonal cycle changes by a factor of three". "What they show is that organics were present early on in Mars".
Questions remain, however, as to how the organic material was formed. "While we don't know the source of the material, the incredible consistency of the results makes me think we have a slam-dunk signal for organics on Mars", Eigenbrode said.
"The detection of organic molecules and methane on Mars has far-ranging implications in light of potential past life on Mars", said Kate. "We thought Mars was dead internally", Harrison said.
"We have no proof that the methane is formed biologically, but we can not rule it out, even with this new data set", Webster said.
He and his colleagues think the methane is coming from underground.
The fact that similar molecules were also present at this new site suggests that this kind of organic material is present in abundance. Organic material can be produced without life. So they looked elsewhere. "But it doesn't tell us that life was there". "And then we went, 'oops, not only did we not find it, but we don't really know what we're looking for if it's not exactly like Earth.' And maybe that was not the best way to go about it".
It "defines how questions will be asked and pursued in the next stage of Mars exploration", Anbar, who was not involved in the study, told AFP by email.
In four locations, including the spot nicknamed Mojave, which Curiosity explored in 2015, the rover discovered thiophenes (molecules that include a ring of carbon and sulphur atoms) and other substances that on Earth can be linked to biological activity.