This undated imagery provided by NASA shows a methane plume in Mars's atmosphere during the planet's northern summer season. This undated imagery provided by NASA shows a methane plume in Mars's atmosphere during the planet's northern summer season. (Trent Schindler/NASA/Associated Press)NASA researchers have found large quantities of methane in the Martian atmosphere, an observation that opens the door to the possibility of microbial life on the planet.

Their findings, published Thursday in the journal Science, show that 19,000 tonnes of methane were released in high concentrations over three specific areas in Mars's western hemisphere. The emissions occurred over a short period in summer 2003.

"This raises the probability substantially that life was there or still survives at the present," study author Michael Mumma of NASA's Goddard Space Flight Center said. "We think the probability is much higher now based on this evidence."

It's possible the gas could have been produced geologically or from active Martian volcanoes, the study authors write.

But methane — produced on Earth by a class of bacteria known as methanogens — could also be produced by bacteria, the researchers say. In the study, they note that over 90 per cent of Earth's methane is produced by living systems.

Mumma said claims of life need far more evidence, however, and this isn't nearly enough.

By 2006, most of the methane had disappeared from the Martian atmosphere, adding to the mystery of the gas, Mumma writes. The researchers also say they don't know whether the methane was ancient or newly produced.

Mumma has reported his team's findings before, but Thursday's publication is the first time they have appeared in a peer-reviewed journal.

Until the study, astronomers had debated whether "whiffs of methane" on Mars were real, said Brown University geologist Jack Mustard, who wasn't part of the research. That debate is pretty much over with this paper, he said.

The methane observations were made by telescopes in Hawaii. The researchers used spectroscopy to examine 90 per cent of the planet's surface over seven Earth years (three Martian years).

With files from the Associated Press