(CNN) - NASA's Curiosity rover encountered something new on the Red Planet last week and the results could potentially have implications for life on Mars.
The rover's tunable laser spectrometer, called SAM, which stands for Sample Analysis at Mars, detected the largest amount of methane ever measured during its mission.
The reading indicated 21 parts per billion units by volume, or ppbv. That means of the volume of air on Mars being assessed, one billionth of the volume of air is methane, the agency said.
So why is this unusually large amount of methane so interesting? On Earth, microbial life is a key source of methane. But the agency also warned that expectations of life should be managed due to the fact that interactions between rocks and water can also create methane, and Mars has water and an abundance of rocks.
"With our current measurements, we have no way of telling if the methane source is biology or geology, or even ancient or modern," said SAM Principal Investigator Paul Mahaffy of NASA's Goddard Spaceflight Center in Greenbelt, Maryland.
The origin of the methane won't be evident right away because the rover doesn't have any instruments that can trace or determine the source. Right now, they can't even be sure that the methane is coming from a spot in the Gale Crater, where Curiosity is located, or emerged from elsewhere on Mars.
This isn't the first time methane has been detected on Mars by Curiosity. Over the course of its mission since landing in August 2012, Curiosity has detected methane many times and studies have been written about how the gas levels actually appear to rise and fall depending on the season.
Curiosity has also picked up on spikes of methane, which occur suddenly, but scientists haven't been able to determine how long the spikes last or why they differ from the known seasonal ups and downs.
The team behind the spectrometer sent an experiment to the rover over the weekend to determine if this is due to a spike, which would appear as a transient plume. Even if no more methane is detected, that could provide more information about the event that was measured.
The science team for Curiosity will take time to study the measurements and prepare for more detections.
They will also reach out to other science teams. The European Space Agency, which launched the Trace Gas Orbiter last year, will be a key collaborator. Their orbiter has yet to detect methane. The two agencies can match up measurements from orbit and the surface.
The two different locations could help scientists determine where gas is originating on the planet and how long it can last in the atmosphere.
Previous detections on Mars
In June 2018, organic matter was found on Mars in soil samples taken from 3 billion-year-old mudstone in the Gale crater by the Curiosity rover. The rover also detected methane in the Martian atmosphere.
The search for life outside Earth focuses on the building blocks of life as we know it, which includes organic compounds and molecules -- although these can exist without life. Organic matter can be one of several things: a record detailing ancient life, a food source for life or something that exists in the place of life.
No matter its purpose, these work as "chemical clues" for researchers studying Mars.
Methane is considered the simplest organic molecule. It's present in other places in our solar system that could host life, like Saturn and Jupiter's moons Enceladus, Europa and Titan. And if life does exist elsewhere, it may be very different or even form differently from how we understand life on Earth.
Over six years, Curiosity has used its Tunable Laser Spectrometer to measure methane in the atmosphere at the Gale Crater. Before, researchers couldn't understand why the little bit of methane detected in the Martian atmosphere varied. With six years of data from a single location, they now have answers.
There is a seasonal variation to the methane that repeats, which means the methane is being released from the Martian surface or from reservoirs beneath the surface. The methane could even be trapped in water-based crystals beneath the surface.
Methane is a strong greenhouse gas, and it could have supported a climate that sustained lakes on Mars. That could even be happening beneath the surface now. The release of methane is an active process on Mars, which could suggest new things about what's unfolding on the Red Planet.
Detecting this organic molecule in the atmosphere, combined with the finding of organic compounds in the soil, has strong implications about potential life on Mars in its past.
The Gale Crater was probably habitable 3.5 billion years ago, based on what Curiosity has shown us. Then, the conditions would have been comparable to Earth. This is also when life was evolving on our own planet.
Knowing that these molecules and compounds were present, then, gives new strength to the idea that life originated or existed on Mars and that more work by the Martian rovers can uncover the past.
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