Program: GN-2011A-Q-78

We propose observations of gaseous methane on Pluto with GNIRS+AO at three specific sub-observer longitudes to (1) establish a baseline for temporal change, (2) search for spatial variability in gaseous methane, and (3) refine the vertical distribution of gaseous CH$_4$. The three longitudes, separated by roughly 120$\deg$, correspond to the longitudes of minimum CH$_4$ frost, maximum CH$_4$ frost, and maximum ratio of nearly pure to highly diluted CH$_4$ frost. These three terrains are expected to produce detectable differences in the gaseous CH$_4$. These observations will provide a temporal and spatial context in which to place the New Horizons encounter with Pluto in 2015.