NASA's Curiosity Rover has been cruising around Mars for nearly six years, and it's stumbled on a few clues — some methane and organic molecules — that could bolster the case for life on Mars.
- NASA's Mars Curiosity Rover has spent years analyzing the red planet's methane levels, and discovered they ebb and flow on a seasonal cycle.
- The rover has also drilled into some ancient rocks called mudstones that hold Earth-like organic and chemical matter inside.
- These clues suggest that the planet might have once harbored life, or still does — but it's too early to draw any big conclusions.
New data collected and beamed back from the rover has given two teams of scientists from NASA new hints about how Mars might harbor key ingredients for microbial, carbon-based life.
The teams, which are studying methane and ancient rocks on Mars, released their findings in two separate papers today. The journal Science published the studies online Thursday afternoon, and the Curiosity Rover's Twitter account quickly posted about them, too.
"Methane swells each summer and ancient carbon-compounds locked in rocks. I haven't found life on Mars, but signs say…we’re on the right track," the Rover tweeted.
Methane on Mars follows the seasons
The first study, led by NASA planetary scientist Chris Webster, represents a kind of sniff test of the red planet.
Scientists used Curiosity to record methane levels in the atmosphere around the rover over the course of four and a half Earth years, or more than two Martian years.
Their data show that methane concentrations change seasonally by a factor of three: Levels in Mars' northern hemisphere ranged from a low of around 0.24 parts per billion in the spring, then nearly tripled to a high of 0.65 parts per billion by the end of summer.
Temperatures on Mars fluctuate between around 67 degrees Fahrenheit at their highest to −243 degrees at their lowest (near the poles), so the researchers think seasonal changes are behind the shifts in methane levels. In the paper, they suggest methane may be locked up underground in water-based crystals called "clathrates." That methane could be slowly seeping out of the clathrates, rising through faults, fractures, and breaches in the rocks — then getting heated up once it reaches Mars' surface.
Methane is important in scientists' search for alien life because it may suggest the presence of life — 95% of the methane on Earth is produced by biological processes.
"It's produced from termites, or rice paddies, or cows, or sheep," Webster said during NASA's livestreamed announcement of the findings.
Certain microbes release methane as a gassy waste or byproduct, so it could serve as an indirect clue of life. However, geologic processes can also make methane.
Webster explained that discovering methane is also exciting because the compound doesn't last more than 300 years.
"If we see methane in the Martian atmosphere, that means something is happening today — it’s being released or it's being created," he said.
Webster and his 43-person team also point out in their study that methane may have helped create past climates on Mars that facilitated the formation of water, since it's a greenhouse gas. This may have been at play in the formation of lakes that are known to have existed on Mars in the past — which can create breeding grounds for microbes.
3-billion-year-old Mars rocks contain Earth-like chemicals and organic matter
Another team of scientists, led by NASA’s Jen Eigenbrode, used the Curiosity Rover to drill 5 centimeters into soil in Mars’s Gale Crater.
The mudstones inside that crater are ancient — more than 3 billion years old. Ashwin Vasavada, a project scientist at NASA's Jet Propulsion Laboratory, explained in the Thursday announcement that Curiosity helped scientists learn that "lakes existed for a long time — for hundreds of thousands if not millions of years" in the crater.
That makes it a promising spot for signs of life to be preserved.
Curiosity extracted some rocks, dumped them into a microwave-sized on-deck sample analysis machine (SAM), and heated them up to analyze any gases that came out of the samples.
The rover found several organic and chemical molecules similar to those you might find on Earth, like stinky dimethyl sulfide that wafts from cooking cabbage, and equally vile methanethiol, which is one of the key compounds in bad breath.
They think these tiny stink-bombs might be fragments of larger organic molecules, suggesting that maybe — just maybe — there was once life on Mars, or even still is.
"Organic matter can directly or indirectly fuel both energy and carbon metabolisms, and in doing so can support carbon cycling at the microbial community level," the authors wrote in their paper.
Other scientists aren’t so sure that these results imply anything certain about life on the red planet.
Seth Shostak, a senior astronomer at the Search for Extraterrestrial Intelligence (SETI) institute, believes we'll find life in space in the next couple of decades, but he cautions that finding indirect evidence of life on Mars doesn't mean Martians exist.
"Chemical evidence, we've been through that before. Even the Viking landers got fooled by some chemical reactions in the dirt," Shostak told Business Insider, referencing the NASA Mars mission from the 1970s.
But he added that it's always gratifying for scientists to learn more about Mars.
"It takes us, maybe, a little bit farther down the yellow brick road in the direction of finding out whether Mars has biology, or ever did have biology," he said. "Knowing more doesn't hurt you, ever."