MAVEN

MAVEN was designed to solve one of the central mysteries of Mars: what happened to its atmosphere. Its name stands for Mars Atmosphere and Volatile Evolution, and its entire purpose was to understand how a planet that once had rivers, lakes, and a thick protective atmosphere became the cold, thin-aired desert we see today. Launched by NASA in November 2013, MAVEN entered orbit in September 2014.

Rather than studying the surface, MAVEN focused on the upper atmosphere and its interaction with the Sun. Its measurements revealed how the solar wind — the constant stream of charged particles flowing from the Sun — strips gas away from the top of the Martian atmosphere and carries it off into space. Crucially, MAVEN observed this escape accelerating during solar storms, providing a direct look at the very process that, over billions of years, robbed Mars of most of its air.

The findings tied together a long-standing story. When Mars lost its global magnetic field early in its history, it lost the shield that had protected its atmosphere from the solar wind. MAVEN quantified how quickly that unprotected atmosphere could erode, helping explain why the planet dried out and cooled. Like other orbiters, MAVEN also serves as a communications relay for surface missions, extending its usefulness well beyond its primary science.