Program: GN-2011B-Q-40

Charon, the largest moon of the dwarf planet Pluto, is a fascinating object, one of the very few trans-Neptunian objects large enough for us to be able to study the ices of its surface. These ices imprint absorption bands on Charon's reflected solar spectrum, which is dominated by water ice. However, near-infrared observations of Charon have shown a 2.21 micron absorption band, attributed to ammonia. Ammonia decreases the melting point of a water ice mix: a sufficiently large TNO, heated during its accretion, could once have had an internal ocean. These may be the signature of ancient cryovolcanic lavas. Unfortunately, this single observed line is ambiguous: its position could be strongly influenced by the ice grains' size and shape. It only provides tantalising evidence for this geophysically important molecule, not confirmation of its presence. Detecting a stronger second line would provide this proof. Laboratory studies show that the deeper fundamental line of ammonia sits at 3-3.1 microns, in L-band. We propose to observe Charon with GNIRS and AO to obtain an L-band spectrum that will decisively confirm if ammonia is present on Charon's surface. This proposal is part of the thesis of the PI.