NASA has discovered fresh evidence that conditions may once have allowed life on Mars to flourish – along with clues that martian organisms might even still be alive today. 

Its robotic rover Curiosity, which has been exploring an ancient lake bed since 2012, found important organic molecules, commonly associated with life, inside ancient rocks.

They show that there was organic chemistry at a time when the surface of Mars was warm and wet, and so suitable for living creatures three billion years ago.

In a separate experiment, Curiosity – also known as Mars Science Laboratory – discovered that levels of methane in the atmosphere vary with the seasons.

This raises the tantalising prospect that it could be being produced right now by living organisms beneath the martian soil.

Scientists cannot be certain that life on Mars is connected with either of the findings because non-biological processes could also be responsible.

But they offer compelling evidence for the possibility of life on Mars and will spur NASA and other space agencies on to make further studies of the Red Planet.

The organic molecules in the rocks within Gale Crater were discovered after Curiosity drilled into mudstone rocks in four separate areas.

The powdered samples collected, which formed from silt at the bottom of the lake billions of years ago, were then heated in the rover’s onboard oven to more than 500 C. That temeprature, which is twice the maximum of a domestic oven, released organic molecules which the rover’s instruments were able to analyse.

Curiosity’s data shows that the lake inside Gale Crater contained all the ingredients needed for life on Mars, including chemical building blocks and sources of energy.

Plumes of methane have previously been detected on Mars by telescopes on Earth. Their origin sparked a debate among scientists because the gas can be produced by rocks as well as microbes.

On Earth methane comes mainly from microbes, including those living in the stomachs of cows and sheep, who belch it into the air.

Mars’s surface is sterile because it has no protection from a deadly bombardment of radiation from space. But some astronomers believe that life on Mars in the form of organisms could survive underground, where they would be shielded from the radiation.

NASA’sassociate administrator for the Science Mission Directorate, 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.”

Jen Eigenbrode of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, who authored one of the two papers appearing in the journal Science, 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.”

She added: “The Martian surface is exposed to radiation from space. Both radiation and harsh chemicals break down organic matter.

“Finding ancient organic molecules in the top five centimeters of rock that was deposited when Mars may have been habitable, bodes well for us to learn the story of organic molecules on Mars with future missions that will drill deeper.”

A new NASA mission, called InSight, is currently en route to Mars to dig deep into its surface. It will land on the Red Planet on November 26 and may tell us more about whether there is or has ever been life on Mars.

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