MAVEN

MAVEN — Mars Atmosphere and Volatile Evolution — launched on November 18, 2013, to answer a planetary cold case: where did the thick, warm atmosphere of ancient Mars go? Orbiting high above the planet since 2014, it measures the upper atmosphere leaking into space, atom by atom, under the constant erosion of the solar wind.

MAVEN’s verdict: Mars lost the bulk of its air to space after its protective magnetic field shut down billions of years ago, with solar storms accelerating the theft. The finding closed the loop on the rovers’ discoveries of ancient lakes below — explaining not just that Mars changed, but how. MAVEN continues today as both scientist and communications relay for the surface missions.