April 2 (UPI) -- Some 15 years ago, a European probe measured traces of methane in the Martian atmosphere. Now, NASA's Curiosity rover and the European Space Agency's Mars Express have confirmed the gas' presence in the air above Gale Crater.
"The presence of methane could enhance habitability and may even be a signature of life," researchers wrote in a new paper published in the journal Nature Geoscience.
On June 15, 2013, NASA's Curiosity rover picked up a methane spike measuring 6 parts per billion in air samples collected and analyzed inside Gale Crater. The next day, ESA's Mars Express probe captured air samples with a methane concentration of 15.5 parts per billion as it whizzed through the atmosphere above Gale Crater.
The independent confirmation by two spacecraft was a coincidence.
"We were very lucky, as this is not the result of coordinated observations," Marco Giuranna, lead author of the new Nature Geoscience paper and a planetary scientist at the Istituto Nazionale di Astrofisica in Rome, told Space.com. "Just by chance!"
To find the likely source of the methane, scientists used computer models to closely analyze the surface structures found in Gale Crater, as well as the surrounding region. Algorithms compared the various surface features to environs on Earth that are known to yield methane emissions.
On Earth, methane is typically a sign of life. But the new analysis suggests a frozen slab of ice or permafrost containing methane, located beneath tectonic faults outside of Gale Crater, is the most logical explanation for the Red Planet's seasonal methane spikes. Scientists estimate periodic melting causes the ice to release the compound in gas form.
At first, scientists thought the methane originated inside Gale Crater.
"Our new Mars Express data, taken one day after Curiosity's recording, change the interpretation of where the methane originated from, especially when considering global atmospheric circulation patterns together with the local geology," Giuranna said in an ESA news release. "Based on geological evidence and the amount of methane that we measured, we think that the source is unlikely to be located within the crater."
The conclusions of the computer simulations aren't definitive, and there is still a lot to learn about Mars' methane. Scientists still aren't sure how methane is removed from the atmosphere and becomes trapped in permafrost.
But the latest findings suggest scientists are getting closer to explaining the methane that Mars Express first measured 15 years ago.
"Our results support the idea that methane release on Mars might be characterized by small, transient geological events rather than a constantly replenishing global presence," said Frank Daerden, researcher at the Royal Belgian Institute for Space Astronomy in Brussels.
Scientists expect to gain new insights into the nature of Mars' methane and other trace gases from data collected by ESA's ExoMars Trace Gas Orbiter, a probe with an instrument suite designed to survey Mars' atmospheric makeup.