Nasa’s Curiosity rover has discovered ‘tough’ organic molecules preserved in three-billion-year-old sedimentary rocks near the surface of Mars and evidence of seasonal variations in methane levels in the atmosphere.

The evidence suggests that the Red planet could have supported both ancient and present life.

Nasa Science Mission Directorate associate administrator Thomas Zurbuchen said: “With these new findings, Mars is telling us to stay the course and keep searching for evidence of life.

“I’m confident that our ongoing and planned missions will unlock even more breathtaking discoveries on the Red Planet.”

To find the organic material, Curiosity drilled into sedimentary rocks called mudstone from four areas in Gale Crater on Mars. The mudstone was created billions of years ago from silt that accumulated at the bottom of an ancient water lake inside the crater.

The rock samples were analysed by SAM, which uses an oven to heat the samples to 500 degrees Celsius to release organic molecules from the powdered rock.

“Organic matter in Martian materials holds chemical clues to planetary conditions and processes.”

Nasa Goddard Space Flight Center representative Jen Eigenbrode said: “Curiosity has not determined the source of the organic molecules.

“Whether it holds a record of ancient life, was food for life, or has existed in the absence of life, organic matter in Martian materials holds chemical clues to planetary conditions and processes.”

SAM has also discovered seasonal variations in methane levels in the atmosphere over a period of around three Mars years, equivalent to nearly six Earth years.

The instrument has detected low levels of methane within Gale Crater that repeatedly peak in summer months and drop in the winter every year.

This methane could have been created by water-rock chemistry, but the possibility of biological origins cannot be discarded.

Methane had previously been detected in Mars’s atmosphere in large, unpredictable plumes.

The latest discoveries are expected to strengthen the prediction that Nasa’s Mars 2020 rover and European Space Agency’s (ESA) ExoMars rover will find more organics on the surface and shallow subsurface of Mars.