Key methane measurements at Mars
This graphic summarises significant measurement attempts of methane at Mars. Reports of methane have been made by Earth-based telescopes, ESA's Mars Express from orbit around Mars, and NASA's Curiosity located on the surface at Gale Crater; they have also reported measurement attempts with no or very little methane detected. More recently, the ESA-Roscosmos ExoMars Trace Gas Orbiter reported an absence of methane, and provided a very low upper limit.
In order to reconcile the range of results, which show variations in both time and location, scientists have to understand better the different processes acting to create and destroy methane.