| Summary: | Living creatures produce most of the methane on Earth. But scientists haven't found convincing signs of current or ancient life on Mars, and thus didn't expect to find methane there. Yet, the portable chemistry lab aboard Curiosity, known as SAM, or Sample Analysis at Mars, has continually sniffed out traces of the gas near the surface of Gale Crater, the only place on the surface of Mars where methane has been detected thus far. Its likely source, scientists assume, are geological mechanisms that involve water and rocks deep underground. If that were the whole story, things would be easy. However, SAM has found that methane behaves in unexpected ways in Gale Crater. It appears at night and disappears during the day. It fluctuates seasonally, and sometimes spikes to levels 40 times higher than usual. Surprisingly, the methane also isn't accumulating in the atmosphere: ESA's (the European Space Agency) ExoMars Trace Gas Orbiter, sent to Mars specifically to study the gas in the atmosphere, has detected no methane. "It's a story with a lot of plot twists," said Ashwin Vasavada, Curiosity's project scientist at NASA's Jet Propulsion Laboratory in Southern California, which leads Curiosity's mission. Methane keeps Mars scientists busy with lab work and computer modeling projects that aim to explain why the gas behaves strangely and is detected only in Gale Crater. A NASA research group recently shared an interesting proposal. Reporting in a March paper in the Journal of Geophysical Research: Planets, the group suggested that methane—no matter how it's produced—could be sealed under solidified salt that might form in Martian regolith, which is "soil" made of broken rock and dust. When temperature rises during warmer seasons or times of day, weakening the seal, the methane could seep out. Led by Alexander Pavlov, a planetary scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland, the researchers suggest the... |