Methane released in Gale crater stays in Gale crater. An overnight change in the Martian atmosphere could hold the gas close to the ground until morning, explaining why the Curiosity rover caught a whiff of methane while an overhead orbiter found none.
The theory offers “a way for the two measurements to live in harmony with each other,” says planetary scientist John Moores of York University in Toronto. He and his colleagues lay out the theory’s details online August 20 in Geophysical Research Letters.
Since 2003, several spacecraft have detected varying amounts of methane on Mars (SN: 1/15/09). NASA’s Curiosity rover, which landed in Gale crater in 2012, has found that amounts of the gas rise and fall in a seasonal cycle (SN: 6/7/18).
Methane should last no more than about 300 years in the Martian atmosphere before sunlight breaks it down. “To see a seasonal cycle tells you that something is actively producing or destroying methane in the present time,” Moores says. Microbes produce methane on Earth, so finding the gas on the Red Planet has been seen as a possible sign of life — although not a definitive one.