In 2020, NASA plans to launch a rover that will seek out organics and search for chemical signatures of life in ancient Red Planet rocks. Methane is another organic molecule. Combined, these results present tantalising hints of a potentially habitable Martian past.
In this handout released by NASA, a Mars landscape is seen in a picture taken by the panoramic camera on the Mars Exploration Rover Spirit January 8, 2003.
To get firmer answers, researchers will need to get equipment to Mars that's sensitive enough to detect life's thumb on the chemical scales.
Since Curiosity landed on Mars in 2012, the rover has been exploring Gale Crater, a massive impact crater roughly the size of CT and Rhode Island, for geological and chemical evidence of the chemical elements and other conditions necessary to sustain life.
First of all, life's "building blocks" would imply something like amino acids or nucleotides.
Want more science from across the ABC? . The rover's Sample Analysis at Mars (SAM) instrument cooked some of the Martian dirt and unlocked some long-hidden carbon-containing molecules, some with sulfur and others with relatively complex structure.
"These spikes and plumes ... they never come back", he said.
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.
Curiosity has detected organics embedded in the sediments of the "Pahrump Hills" area of Gale Crater. In the winter, this count ebbs by a factor of three to 0.2 parts per billion. "We know that on Earth microorganisms eat all sorts of organics", said Jen Eigenbrode, a biochemist at the space agency's Goddard Space Flight Centre. Perhaps it's some geologic process.
This seasonal pattern seems to imply that temperature changes might be triggering the seasonal release, the scientists said, suggesting that the methane might be stored in water-based crystals called clathrates. The seasonal variation provides an important clue for determining the origin of martian methane. However, the abundances of methane measured are greater than models predict should occur, meaning we still don't know exactly how they are produced. All we can say from the data is that there is complex organic matter similar to what is found in many equivalent aged rocks on the Earth. But for now, there's no evidence for any such bacteria. "We thought Mars was dead internally", Harrison said.
All of which will be taken into account when several more Mars lander projects head for the Red Planet in the next two years.
Methane is considered the simplest organic molecule. In an accompanying article, Inge Loes ten Kate of the Department of Earth Sciences in the Netherlands' Utrecht University described them as "breakthroughs in astrobiology". The mission's Trace Gas Orbiter arrived at Mars in late 2016, and it's now collecting data that will let scientists map Mars's methane-and maybe even pinpoint its sources.
"We don't know if that methane is ancient, we don't know if it's modern - it could be either", Webster said. But they aren't proof of life on Mars, or even necessarily strong evidence that there's anything living, or anything that used to be alive, out there.
The results revealed a wealth of organics, Eigenbrode said - including some that had carbons linked in ring structures (such as benzenes) and others that include carbon chains (such as propane). A deeper understanding of our universe and our place in it?