Detecting methane on Mars is hard, even for a rover in the thick of it. Curiosity can’t just hold some litmus paper to the wind until it senses methane and changes color. In one method, the rover ingests some air into an analysis unit and scrubs out all the carbon dioxide, which makes up the majority of the Martian atmosphere. The unit concentrates the gases that remain, amplifying their signals, and teases out the methane.
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The latest spike was found this way. It was three times the size of the 2013 detection, and Mahaffy said the team was “dumbfounded.” Scientists even scrapped the upcoming days’ rover experiments in favor of running the test again. When the data came back, the plume of methane had disappeared. The atmosphere around the rover appeared to have reverted to its usual state, with low background levels of methane. Curiosity scientists now believe that the spike is similar to other promising but short-lived detections.
The Curiosity rover is not equipped to further probe the mystery of methane on Mars, or the question of potential methane-producing beings. Although the rover’s instruments are designed to pick up methane, they can’t determine its source. NASA’s next rover, known for now as Mars 2020, won’t carry any methane-detecting instruments; when it arrives in early 2021, it will search for signs of ancient life, and any methane it produced would be long gone. Neither will Europe’s planned rover Rosalind Franklin, named for the chemist who helped unlock the secrets of DNA, when it touches down around the same time.
Methane can be detected from above, too, by orbiters circling Mars that study how the gas interacts with sunlight. Mars Express, a European Space Agency orbiter, picked up the same plume Curiosity registered in 2013. The Trace Gas Orbiter (TGO), another European spacecraft, is among the newest on and around Mars, and its instruments might be sensitive enough to provide some information about the source of a potential methane detection. “TGO may be able, if the gas comes in sufficient high concentration, but it is hard,” says Håkan Svedhem, the mission’s project scientist.
The TGO flew over the crater where Curiosity resides and made the latest detection, but Svedhem and European scientists haven’t responded to questions about whether the orbiter sensed it, too.
One of the best ways to answer the methane question is also one of the most ambitious: Drill deep into the Martian terrain, scoop up some material, and hurl it back toward home. Space agencies are still years away from this kind of sample-return mission, which would involve launching a rocket from the surface of Mars, something no one has ever tried before. And even if methane-releasing bacteria squirm beneath the surface, the most advanced technology might still miss the mark. “The problem with drilling a hole or two is, what if you miss?” says Paul Niles, a planetary geologist at NASA. “The bacteria might be concentrated in one area, and you might miss it if you drilled in the wrong place.”