While the absence of methane doesn't entirely preclude the possibility of present-day life on Mars, it does present a setback to researchers, The New York Times reported.
"You don't have direct evidence that there is microbial process going on," said Sushil Atreya, a professor of atmospheric and space science at the University of Michigan and a member of the science team.
John Grotzinger, NASA's project scientist for the Curiosity mission, said the lack of methane "discounts" the possibility of creatures living on Mars.
"It does diminish the argument that there are methanogenic organisms there," Grotzinger said.
Ten years ago, observations from telescopes on Earth and a spacecraft orbiting Mars suggested plumes of methane were rising from certain regions, but Curiosity's readings debunked those determinations.
"It just isn't there," Atreya said of the methane.
Atreya said he originally thought highly reactive chemicals on the Martian surface could be destroying methane, but later determined that theory wasn't "panning out."