In the distant past, both Earth and Mars were covered in thick atmospheres and held large bodies of water. While Earth has become a cradle of life in our solar system, Mars lost its atmosphere and became a barren, desert world. No one knows why. NASA's 2013 MAVEN mission will offer scientists many clues as they try to solve this Martian mystery.A few years ago, NASA put out a call for mission proposals to explore the Martian atmosphere. They wanted to do it as inexpensively as possible, with a robust mission plan that had a "low implementation risk." In other words, it'll be tough to screw up. They chose MAVEN over more complicated proposals like the Aerial Regional-scale Environmental Survey of Mars (ARES, pictured) because it's basically a satellite that will orbit Mars for a year and report back what it finds. As it orbits the Red Planet, MAVEN, which is the somewhat tortured acronym for "Mars Atmosphere and Volatile EvolutioN," will use a suite of eight instruments to sample the atmosphere. It will track the composition of the Martian air and create a precise record of current atmospheric loss on Mars. That will give scientists a window to Mars' mysterious past. One theory suggests that the loss of the planet's magnetic field led the atmosphere to be stripped away. Image by: NASA. NASA Selects 'MAVEN' Mission to Study Mars Atmosphere. [NASA]