NASA scientists report that the Curiosity rover has found new evidence preserved in rocks on Mars that suggests the planet could have supported ancient life, as well as new evidence in the Martian atmosphere that relates to the search for current life on the Red Planet.
Right off the bat, scientists have made it clear that none of this is necessarily evidence of life itself, and the rover has not discovered life on the red planet either past or present.
But scientists say the findings are a good sign for future missions exploring the planet's surface and subsurface in the quest for life.
The new findings, in two different papers, describe “tough” organic molecules in three-billion-year-old sedimentary rocks near the surface, as well as seasonal variations in the levels of methane in the atmosphere.
Both papers appear in the June 8 edition of the journal Science.
Organic molecules contain carbon and hydrogen, and also may include oxygen, nitrogen and other elements.
While commonly associated with life, scientists say organic molecules also can be created by non-biological processes and are not necessarily indicators of life.
They stress the fact that the rover has not determined whether the organic molecules it has discovered point to any specific source, either biological or geological.
Those inroads may lie in future missions, such as the Mars 2020 mission.
The methane mystery is described in the second paper appearing in Science.
NASA scientists describe the discovery of seasonal variations in methane in the Martian atmosphere over the course of nearly three Mars years, which is almost six Earth years.
This variation was detected by Curiosity’s Sample Analysis at Mars instrument suite.
Scientists say water-rock chemistry might have generated the methane, but they add that they cannot rule out the possibility of biological origins.
Methane previously had been detected in Mars' atmosphere in large, unpredictable plumes.
Scientists say this new result shows that low levels of methane within Gale Crater repeatedly peak in warm, summer months and drop in the winter every year.
They say the most likely source for the methane is a sub-surface reservoir ... possibly geological, and possibly biological.
It remains a singularly tantalizing fact that biological origins cannot be ruled out as a source for the seasonal changes in methane levels.
Although the surface of Mars is inhospitable today, scientists confirm that 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.
Data from Curiosity reveal that billions of years ago, a water lake inside Gale Crater held all the ingredients necessary for life, including chemical building blocks and energy sources.
Curiosity is currently in Gale Crater, continuing its investigation of the ancient sediments there.
The spacecraft has been at work for roughly five years, even though it was designed for a mission duration of somewhere in the neighborhood of between 90 and 100 days.