"Both these findings are breakthroughs in astrobiology", writes Utrecht University geoscientist Inge Loes ten Kate in this week's issue of Science.
"What this new study is showing in some detail is the discovery of complex and diverse organic compounds in the sediments".
The samples were found to contain thiophene, 2- and 3-methylthiophenes, methanethiol, and dimethylsulfide. And now they've added a catalogue of organic molecules to that list.
"When you work with something as insane as a rover on Mars, with the most complex instrument ever sent to space, it seems like we're doing what may have been perceived earlier as impossible", says lead author Jennifer Eigenbrode, a biogeochemist at NASA Goddard.
Over almost six years roaming the surface of Mars, NASA's Curiosity rover has detected organic molecules that offer a taste of what an ancient life-friendly Red Planet might have looked like.
In addition, methane's observed behavior on Mars is freakish. Another noticed the methane levels around Curiosity varied by the season.
Just a couple of weeks ago, NASA announced that Curiosity had successfully drilled a hole using this new technique, and its handlers were excited that the rover could get back to work. Gale Crater's rim is visible on the horizon.
Future missions will help. Each martian summer, the atmosphere's methane concentration rises to about 0.6 parts per billion.
"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).More news: LeBron James Shouldn't be the Finals MVP
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"This is all possible because of Curiosity's longevity". Researchers said they can't rule out a biological source. This is close to the amount observed in Martian meteorites and about 100 times greater than prior detections of organic carbon on Mars' surface.
These might explain the increase in molecules, but they do still leave its rapid vanishing act wanting of an explanation.
There's so much left to learn about Mars. The seasonal variation provides an important clue for determining the origin of martian methane. Here it is retained by the soil until the temperature increases sufficiently to release the gas.
A crystalline water structure called a clathrate provides a flawless explanation.
Curiosity's methane measurements occurred over four-and-a-half Earth years, covering parts of three Martian years. Or reactions driven by Mars's ancient volcanoes could have formed the compounds from primordial carbon dioxide. The methane could even be trapped in water-based crystals beneath the surface.
That's why one of the scientists they quote says, "I suspect it's geological".
"The thing about the chlorinated molecules is that it's not what you'd typically find in natural samples, and so we weren't sure what the significance was at the time", Jennifer Eigenbrode of NASA's Goddard Space Flight Center in Maryland, lead author of one of the papers, said in a briefing.
The scientists hope to find better preserved organic compounds with Curiosity or other rovers that would allow them to check for chemical signatures of life. There's also the chance the rovers will dig up fossilised evidence of life.
The Mars 2020 rover won't represent the first jump in camera improvement as the Spirit and Opportunity rovers had 10 each, and the Curiosity rover had 17. That's particularly exciting since water ― so far as we know ― is also an essential ingredient for life.