There is a methane situation on Mars. Maybe. NASA’s Curiosity rover has detected methane on the planet, which excites researchers to no end, but some believe that the methane samples the rover is picking up are actually coming from the rover itself. The question of methane on Mars has been a mystery for decades, and it seems researchers may not really be any closer to solving it.

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Methane on Mars isn’t a new mystery. In fact, it’s been nearly 50 years since the Mariner 7 spacecraft first detected methane near the south pole of the red planet. A month later, the research team figured out those signals actually came from carbon dioxide ice, but that didn’t quell the curiosity. Since that time, researchers have been determined to confirm whether, and how much, methane exists on Mars. And why the huge interest piqued by this fairly common gas? Simple. The presence of methane could suggest the presence of living organisms.

In 2003 and 2004, reports of a large methane cloud near Mars were observed by earthbound telescopes and orbiting spacecraft. Researchers experienced a renewed enthusiasm in the possibility of life on Mars, and the Curiosity rover became the focal point as it gathered samples over the course of several months in 2013 and 2014. Although no methane turned up in any of those samples, others collected just a short while later did reveal methane. But where did it come from?

Related: NASA’s Curiosity rover finds water on Mars

The research team is well aware that the Curiosity rover emits methane, but they are insistent that the earthly methane aboard the rover is not interfering with the samples from the red planet. Paul Mahaffy, the principal investigator on Curiosity’s Sample Analysis at Mars (SAM) suite of instruments says, “It seems unlikely that after more than a year on the surface of Mars a sudden source of methane from the spacecraft would appear, persist for 60 days and then disappear,” he says. “Methane is a very volatile gas, and any residual methane brought to Mars should be long gone.” It sounds logical, but skeptics warn that it’s too difficult to rule out the rover completely as the source of methane.

The rover continues to look for methane in the likeliest of places, such as in fresh craters on the surface of the planet. Unfortunately, the most probably source of methane on Mars is carbonaceous meteorites, which emit a plume of methane when broken down by ultraviolet radiation. They also, however, tend to break apart in the atmosphere and rain down in a shower of tiny fragments, making them more or less undetectable. Based on that information, it’s uncertain where the trail of methane will lead, if not straight back to Curiosity.

Via Discovery

Images via NASA