That doesn't mean they've found life, but it's a good indication Mars could have sustained life in the past. This includes findings about Mars' atmosphere and organic matter preserved in 3-billion-year-old mudstones in the Gale crater. That leaves open the possibility that microorganisms once populated our planetary neighbour and still might.
This is the first time we've seen something repeatable in the methane story, so it offers us a handle in understanding it.
As seasons come and go on Mars, NASA's Curiosity Rover has been diligently sniffing and digging away, looking for signs the planet could have supported life. While commonly associated with life, organic molecules also can be created by non-biological processes and are not necessarily indicators of life, NASA says.
A self-portrait of NASA's Curiosity Mars rover. The scientists took questions from the public as they revealed increasingly more information about Curiosity's latest developments.
The new findings are also detailed in two studies published Thursday in the journal Science. Together, the researchers believe these findings to be "breakthroughs in astrobiology". "What they show is that organics were present early on in Mars".
"The detective work they did is worthy of Sherlock Holmes", said Katherine Freeman, a professor of geosciences at Pennsylvania State University who was not involved with the research. Yet when NASA's twin Viking probes landed on Mars in 1976, their studies suggested something startling: Martian soil, it seemed, contained less carbon than lifeless lunar rocks.
"The big takeaway is that we can find evidence". But scientists revealed tantalizing hints about present-day Mars today, too. Methane is ubiquitous in places like the atmospheres of gas-giant planets.
"If there are no organics, we can pretty much forget about there being life or ever having been life on Mars", says Dr. Weintraub.
Curiosity's methane measurements occurred over four-and-a-half Earth years, covering parts of three Martian years.
Methane, the simplest organic molecule, ranges "between 0.24 to 0.65 parts per billion, peaking near the end of summer in the Northern hemisphere", said the report, based on three years of data. "It's tripling ... that's a huge, huge difference". The two rock samples, from sites named Confidence Hills and Mojave, are at the bottom of Gale Crater. The diameter is slightly smaller than a US dime.
The methane study, spearheaded by JPL atmospheric scientist Chris Webster, is also intriguing for astrobiologists. The gas creeps from below the surface up to be released into the Mars atmosphere via riverbeds, cracks, and crevices in the surface of the planet.
"We don't know if that methane is ancient or modern", Webster said in a press conference.
Regardless, the detection is a technical achievement, said Williford, because it demonstrates that organic molecules can persist near Mars's surface for billions of years.
As with methane, there could well be non-biological explanations for the presence of carbon-containing molecules on Mars, such as geologic processes or impacts by asteroids, comet, meteors and interplanetary dust.
NASA's Jennifer Eigenbrode said in an interview this year, 'I look at organic molecules in rocks, ice and sediments and try to figure out where they came from and what happened to them over time. Answers to life's biggest questions? What is needed to find more clues is a mission to Mars with a deep drill.
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