In findings that are as scientifically significant as they are crushing to the popular imagination, NASA reported on Thursday that its Mars rover, Curiosity, which has been trundling across the red planet for a little more than a year, has deflated hopes that life could be thriving on Mars today.

The conclusion, published in the journal Science, comes from the fact that Curiosity has been looking for methane, a gas that is considered a possible calling card of microbes, and has so far found none of it.

While the absence of methane does not entirely preclude the possibility of present-day life on Mars — there are plenty of microbes, on Earth at least, that do not produce methane — it does return the idea to the realm of pure speculation without any hopeful data to back it up.

“You don’t have direct evidence that there is microbial process going on,” said Sushil K. Atreya, a professor of atmospheric and space science at the University of Michigan and a member of the science team.

But NASA scientists are going strictly by their data. John P. Grotzinger, the project scientist for the Curiosity mission, would only go so far as to say that the lack of this gas “does diminish” the possibility of methane-exhaling creatures going about their business on Mars.

Curiosity made measurements from Martian spring to late summer, coming up empty for methane.

Scientists have long thought that Mars, warm and wet in its early years, could have been hospitable for life, and the new findings do not mean that it was not. But that was about 3 1/2 billion years ago. — New York Times News Service