That leaves open the possibility that microorganisms once populated our planetary neighbour and still might. Are they from life?'
The new evidence comes from a pair of rocks. If scientists keep drilling deeper and more widely, as they plan to do with the European and Russian space agencies' ExoMars rover and NASA's Mars 2020 mission, who knows what they might find?
Powder from the rocks went into an analyzer on the rover called SAM that can determine what they were made of. So NASA astrobiologist Jennifer Eigenbrode at the Goddard Space Flight Center spent the intervening years figuring out which signals were clearly junk and removing them. But for this sample, Eigenbrode and her colleagues only analyzed the gases that were released above 400 degrees Celsius. "This gives us a lot of hope going forward in terms of organic detection on Mars", Dr. Pontefract says. The so-called "tough" molecules include carbon and hydrogen, and may also contain oxygen, nitrogen, and other building blocks of life.
"Although the surface of Mars is inhospitable today, there is clear evidence that in the distant past, the Martian climate allowed liquid water - an essential ingredient for life as we know it - to pool at the surface", NASA reports. "It's step by step", she says. Meteorites are constant pummeling Mars, and many of them contain carbon. This mudstone gradually formed billions of years ago from silt that accumulated at the bottom of the ancient lake.
The space agency has not divulged specific information about what it may have found, leaving many to wonder what intriguing details will be learned about the red planet. And they believe the fragments could have been parts of larger molecules present a long, long time ago on Mars. It could be. Organic molecules are the building blocks of all known forms of life.
The latest data shows huge swings in the level of methane in the atmosphere as the seasons change, and new types of organic molecules capable of preserving life just beneath its surface.
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. There may be more material buried deeper.
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.
Methane in the martian atmosphere has been detected before, but only in isolated patches or plumes of higher concentrations, not in any repeatable pattern. Mars2020 will shed light on the organic molecules-and prepare a sample that some future mission could bring back to Earth. "So way under the ground this methane is trapped".
The source is still unclear, but it may be stored in the cold Martian subsurface in water-based crystals called clathrates, researchers said. "So it holds it in the winter time and releases it in the summertime as temperatures get warmer".
And if you're a scientist searching for signs of life, organic matter hopefully points to, if not a direct indication of life itself, something like life, or something other life forms can live off.