The discovery leaves open the possibility that microorganisms once populated the red planet - and still might.
These organic compounds, a requirement for life as it's known on Earth, were found in 3-billion-year-old rocks deposited on the floor of Gale Crater. This latest discovery adds evidence that Mars may have been capable of supporting life in its ancient past, though there's still no evidence that life had actually existed on the Red Planet. NASA also announced it had found signs of "seasonal methane" in the Mars atmosphere. While water-rock chemistry might have produced those variations, NASA said it "cannot rule out the possibility of biological origins".
In 2015, however, Curiosity made the first tentative detection of organic molecules on Mars, finding evidence of chlorine-contaminated carbon compounds in soil samples heated to more than 800 degrees Celsius in SAM.
Now, samples taken from two different drill sites on an ancient lakebed have yielded complex organic molecules that look strikingly similar to the goopy fossilized building blocks of oil and gas on Earth.
The new results represent the longest systematic record of atmospheric methane, with measurements taken regularly over five years. Over the intervening years, fluid flowing thought it would have initiated chemical reactions that could have destroyed the organic matter - the material discovered may in fact be fragments from bigger molecules.
Q: What could be the possible sources for these organic molecules, biological or otherwise?
One thing is for sure, though - whatever we can figure out about the chemistry of Mars, it's nearly certainly going to add precious details to our understanding of life in the cosmos. That's because the surface of Mars is constantly bombarded with radiation that can break down organic compounds.
In the first study, a team led by Christopher Webster, a chemist at NASA's Jet Propulsion Laboratory in California, describes how Mars' atmosphere appears to have low levels of fluctuating methane.
But it's getting easier to hypothesise that Mars once harboured life, because Curiosity's extended trundling on Mars has shown evidence of liquid water on the surface and found plenty of the chemicals that you'd expect as pre-cursors to, or by-products of, life. What the authors have found is a systematic variation in methane concentration with season, with the highest concentrations occurring at the Gale Crater towards the end of the northern summer. On Mars, that's been a maddening challenge: While scientists have detected bursts of methane on the planet, they've appeared at random - and thus, it's been hard to figure out what the source is. Certainly, there are geological processes that could make methane levels change over the Martian year, she said. One of their most hard tasks is to prove that the carbon they find is biogenic, and not produced through non-living, geological processes. Hell comes from Mars, NASA, and it's only been two years since we cleaned up the last incident of Mars Hell. They therefore suggest that methane could be trapped at depth, gradually seeping to the surface. Curiosity can only drill a few centimeters into Martian rocks, and it lacks the advanced tools necessary to search for more complex markers of life. This doesn't constitute proof that life existed on Mars, though.