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For more than a year, a 3.5-tonne spacecraft has been circling Mars in a series of erratic loops. Now, after 1,000 circuits, the Trace Gas Orbiter (TGO) has reached the ideal position to study the planet’s atmosphere, and has made its first scientific observations. It is poised to solve one of the most controversial mysteries in Martian science: why methane, a possible signature of life, is being released on the red planet.