A decade and a half ago, three teams of scientists reported that they had detected methane in the Martian atmosphere. Two used observations from Earth, and the third used data from Mars Express. All of the measurements were at the edge of the instruments’ capabilities.

Two years later, the methane seemed to have disappeared. If that finding was accurate, it suggested not only that something was creating methane on Mars, but that something else was quickly destroying it.

The Curiosity mission initially cast more doubt on the methane claims, as it detected very little of the gas, about 0.7 parts per billion. Then in 2013, the levels jumped by a factor of 10. The following January, levels fell back to below 1 part per billion. The methane disappeared so quickly, and the usual levels are so low, that scientists are now trying to explain how methane could have been destroyed so quickly.

In the new research, the scientists looked at passes that Mars Express made over Gale Crater during the first 20 months of Curiosity’s mission. For all but one of the orbiter’s observations, no methane was detected. But on June 16, 2013, the instrument measured about 15 parts per billion of methane. A day earlier, Curiosity had also measured elevated methane.

“It reaffirms the hypothesis that Mars is presently active,” said Sushil Atreya, a planetary scientist at the University of Michigan and a member of the Curiosity science team.

The Mars Express findings also point to a possible source of the methane, about 300 miles east of Gale. In that region, ice must exist just below the surface. “That methane could be released episodically along faults that break through the permafrost due to partial melting of ice,” Dr. Giuranna said.

If true, that could be a tempting site for a future spacecraft to untangle the methane mystery.

Dr. Atreya is less certain of that conclusion, which involves assumptions about Martian weather. The Curiosity scientists thought the methane originated within Gale, to the north of the rover.