Washington ? A surprising and mysterious belch of methane gas on Mars hints at possible microbial life underground, but also could come from changes in rocks, a new NASA study found.

The presence of methane on Mars could be significant because by far most of the gas on Earth is a byproduct of life — from animal digestion and decaying plants and animals.

Past studies indicated no regular methane on Mars. But new research using three ground-based telescopes confirmed that nearly 21,000 tons of methane were released during a few months of the late summer of 2003, according to a study published Thursday in the online edition of the journal Science.

“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 told The Associated Press.

But Mumma also said claims of life need far more evidence 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, he said.