The Martian surface bears ample evidence of flowing water in its youth, from crater lakes and riverbeds to minerals that only form in water. But today Mars is cold and dry, and scientists think that the loss of Mars' water may have been caused by the loss of its early atmosphere. NASA's Mars Atmosphere and Volatile EvolutioN mission, or MAVEN, will be the first spacecraft devoted to studying the Red Planet's upper atmosphere, in an effort to understand how the Martian climate has changed over time.
Credit: NASA/Goddard Space Flight Center
