In findings that are as scientifically significant as they are crushing to the popular imagination, NASA reported Thursday that its Mars rover, Curiosity, 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 rule out 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.

The history of human fascination with the possibility of life on Mars is rich, encompassing myriad works of science fiction, Percival Lowell’s quixotic efforts to map what turned out to be imaginary canals, Orson Welles’s panic-inducing 1938 “War of the Worlds” radio play, and of course Bugs Bunny’s nemesis, Marvin the Martian.

But Marvin apparently did not emit enough methane for Curiosity’s sensitive instruments to find him.