Scientists say initial sampling of Mars' atmosphere by the NASA rover Curiosity did not definitively detect methane, a gas that can be a clue to determining if the red planet ever was hospitable to microbial life.
Test results released Friday in a teleconference from Jet Propulsion Laboratory are not conclusive but are in line with past studies that found no regular methane on Mars.
The results do stand in contrast to other research such as observations by Earth-based telescopes that indicated Mars belched thousands of tons of methane in 2003.
On Earth, methane gas is overwhelmingly a byproduct of life, but it can also be produced by non-biological processes.
Mission scientists will continue to search for methane.
Curiosity has been operating on Mars since its August landing in a crater.