The philosophy of NASA's Mars Program has been "Follow the water," but "Where did the atmosphere go?" is still a lingering question. Although fluvial features such as dry riverbeds are visible on Mars, the atmosphere today is too thin to support liquid water, implying that Mars once had a thicker atmosphere that was lost to space. NASA's Mars Atmosphere and Volatile EvolutioN Mission, or MAVEN, will test this hypothesis. As part of its remote sensing instrument package, MAVEN's Imaging Ultraviolet Spectrograph (IUVS) will look at isotopic hydrogen ratios in the upper atmosphere of Mars, helping scientists to determine just how much water once flowed across the Red Planet.
MAVEN will use its Imaging Ultraviolet Spectrograph (IUVS) to study the upper atmosphere of Mars in unprecedented detail, helping scientists to determine what happened to the planet's ancient atmosphere - and its liquid water.
GCMD keywords can be found on the Internet with the following citation:
Olsen, L.M., G. Major, K. Shein, J. Scialdone, S. Ritz, T. Stevens, M. Morahan, A. Aleman, R. Vogel, S. Leicester, H. Weir, M. Meaux, S. Grebas, C.Solomon, M. Holland, T. Northcutt, R. A. Restrepo, R. Bilodeau, 2013. NASA/Global Change Master Directory (GCMD) Earth Science Keywords. Version 220.127.116.11.0