The discovery leaves open the possibility that microorganisms once populated the red planet - and still might.
The complex organic matter was found buried - and preserved - in ancient, three-billion-year-old sediments, suggesting that the planet could have once been home to life. Today, scientists are announcing they've discovered conclusive evidence that several organic compounds are indeed found on the Red Planet.
This diagram shows how methane beneath the Martian ground might find its way to the surface, where its uptake and release could produce the large seasonal variation in the atmosphere that was observed by the Curiosity rover. Researchers said they can't rule out a biological source.
Curiosity, which has been exploring Gale Crater since it landed in 2012, has previously dug up signs of organic molecules in the ancient lakebed, by taking rock samples and subjecting them to the suite of laboratory instruments in its belly.
But finding a trove of organic molecules on Mars is a big breakthrough for astrobiology, as organic molecules could be food for microbes, even if it doesn't represent life itself.
While we know that Mars was habitable in the past, the case demonstrates just how hard it will be to ever prove the existence of past life on its surface. Mars2020 will shed light on the organic molecules-and prepare a sample that some future mission could bring back to Earth.
Furthermore, Pontefract says, ExoMars and NASA's Mars 2020 mission will use tools that take a different approach to analyze organics. "We can find organic matter preserved in mudstones that are more than three billion years old", Siebach said.
The team picked up a welter of closely related organic signals reflecting dozens or hundreds of types of small carbon molecules, probably short rings and strands called aromatics and aliphatics, respectively. Kerogen is a name given to organic material that is present in rocks and in carbonaceous meteorites.
"We don't know if that methane is ancient or modern", Webster said in a press conference. It means that, one day, there is potential for more sophisticated instrumentation to detect a wider range of compounds in Mars samples, including the sorts of molecules made by living organisms, such as lipids, amino acids, sugars, or even nucleobases.
Dr Webster said the difference was much larger than what you would expect if the methane was produced by the breakdown of organic matter from space. "And the last one is geological processes, meaning the rock-forming processes themselves".
Mineral veins on Mars seen by Curiosity. Specifically, NASA says that lower levels of methane were found to decrease in the winter and peak in the summer on an annual basis. What the study has done, though, is to propel the search for life on Mars higher up the list of global space exploration priorities - giving space agencies ammunition to argue for a coordinated programme of missions to explore the Red Planet. After drilling, Curiosity heats the rock samples, releasing the compounds.
This work was funded by NASA's Mars Exploration Program for the agency's Science Mission Directorate (SMD) in Washington. We also know that Mars was once warmer and had a denser atmosphere, important requirements for life as we know it.
Webster theorizes the methane created either now or long ago is seeping from deep underground reservoirs up through cracks and fissures in the crust.
Ever since the twin Viking landers touched down in 1976, scientists have hunted for signs of organic molecules on Mars.