MAVEN — Mars Atmosphere and Volatile Evolution — lifted off atop an Atlas V rocket to investigate the thin Martian atmosphere and the solar wind's role in stripping it away over billions of years. After a ten-month cruise, it entered Mars orbit in September 2014, providing evidence that solar radiation had gradually eroded the planet's once-thicker atmosphere, helping explain how a once-wetter Mars became the arid world seen today.
Mars presents one of planetary science's great puzzles: orbital and rover imagery clearly shows ancient riverbeds, lake basins, and mineral deposits that could only have formed in the presence of abundant liquid water, yet the modern Martian atmosphere is so thin that liquid water cannot persist on the surface today. MAVEN was designed specifically to explain the disappearance.
Launched from Cape Canaveral on an Atlas V, the spacecraft carried instruments to measure the upper atmosphere and its interaction with the solar wind, the constant stream of charged particles flowing from the Sun. Unlike Earth, Mars lacks a global magnetic field to shield its atmosphere, leaving it exposed to this erosive bombardment over geological time.
After arriving in Martian orbit in September 2014, MAVEN detected evidence that solar wind and radiation were indeed stripping gas from the atmosphere at a measurable rate, and that this process, extrapolated backward over billions of years, could account for the transformation of an early Mars with a thick atmosphere and surface water into the cold desert world humanity now sends rovers to explore.