On Mars, methane could be a potential biosignature, a chemical trace produced by life. However first, scientists must rule out methane's nonbiological origins.

To investigate where the methane emissions could originate, the researchers employed a method called "back-trajectory analysis." This method involves using models based on what scientists know about Mars's atmosphere to track a parcel of air backward in time from the moment of its measurement. The researchers studied all seven methane spike events that have been detected so far and used an existing global climate model of Mars to simulate how wind could transport methane traveled around the planet.

By simulating the backward trajectory of each spike of methane on the basis of wind patterns from various seasons and times of day, the authors found that the spikes most likely originated from the same general area: the northwestern part of Gale crater, a large impact crater that scientists think once held liquid water, where Curiosity is currently exploring.

However, Curiosity's detections of methane on Mars have been called into question by experts. For instance, the European-Russian ExoMars Trace Gas Orbiter (TGO), which has been investigating the Red Planet from orbit since late 2016, hasn't detected the same abundance of methane in Mars's atmosphere that Curiosity has detected from the surface. The authors note there could be a geological mechanism that quickly sequesters methane from the atmosphere or an atmospheric mechanism trapping it near the surface. Further research needs to be done to confirm that this is where the methane originates, the authors note, and Curiosity should continue making measurements of ambient methane abundance to capture more methane spike events.

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