Two studies shed light on the theory that Mars may have once been an inhabited world. Curiosity rover just found organic matter in the Martian soil.

NASA’s Mars rover Curiosity has identified a variety of organic molecules on 3 billion-year-old mudstone in the Gale crater. The rover has also detected methane concentrations in Mars’ atmosphere, NASA announced Thursday.

Researchers also detailed their new findings in two studies published Thursday in the journal Science.

The Organic Matter

The rover dug just 2 inches (5 cm) into the mudstone, a fine-grained sedimentary rock, at Gale Crater. Thus, finding three different types of organic molecules. Gale Crater is probably the site of a large lake when ancient Mars was warmer and wetter than the desolate planet it is today.

“There’s three possible sources for the organic material,” said astrobiologist Jennifer Eigenbrode of NASA’s Goddard Space Flight Center in Maryland. “The first one would be life, which we don’t know about. The second would be meteorites. And the last one is geological processes, meaning the rock-forming processes themselves.”

However, the new discovery doesn’t necessarily prove the evidence of life itself.

“While not necessarily evidence of life itself, these findings are a good sign for future missions exploring the planet’s surface and subsurface,” NASA has written on their website.

“We cannot rule out the possibility that it was created biologically,” said study lead author Chris Webster, a senior research fellow at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California. “We can’t say that it was, but we’re certainly not dropping that idea. So, in a sense, that’s positive for the astrobiologists in the world.”

The rover touched down inside Mars’ huge Gale Crater for the first time in August 2012. NASA’s rover made the first definitive detection of organic molecules back in 2014. But it was a much more limited set of compounds.

“What the organic detections in the rock do is to add to the story of habitability. It tells us that this ancient environment on Mars could have supported life,” Eigenbrode said. “Everything that was needed to support life was there. But it doesn’t tell us that life was there.”

Finding Methane in the Air

Also, the other story led by Webster, published in the second paper, describes 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. Curiosity rover detected the variation with its Sample Analysis at Mars (SAM) instrument suite.

The researchers found that these concentrations ranged a great deal, from a low of about 0.24 ppb to a maximum of 0.65 ppb. Water-rock chemistry might have generated the methane. But scientists cannot rule out the possibility of biological origins.

“This is the first time we’ve seen something repeatable in the methane story, so it offers us a handle in understanding it,” said Chris Webster of NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California, lead author of the second paper. “This is all possible because of Curiosity’s longevity. The long duration has allowed us to see the patterns in this seasonal ‘breathing.'”

So, by finding that these molecules and compounds were present, the idea that life originated or existed on Mars becomes more clear.

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Thumbnail image: This low-angle self-portrait of NASA’s Curiosity Mars rover shows the vehicle at the site from which it reached down to drill into a rock target called “Buckskin” on lower Mount Sharp. Credits: NASA/JPL-Caltech/MSSS