USING COMPOSITION AND MORPHOLOGY TO LEARN ABOUT PROCESSES AT WORK IN THE PLUTO SYSTEM

Wherever they occur in planetary surface environments, mobile, volatile materials enable distinct geology. In addition to their own deposits, they can also mobilize otherwise inert materials. Pluto's gravitationally bound volatiles include N₂, CH₄, and CO. These exist mostly as ices on Pluto's cold surface, though their vapor-pressure supports a low-pressure atmosphere.

NASA's New Horizons probe flew through the Pluto system in 2015, performing the first up-close reconnaissance of this previously unexplored class of planet. The spacecraft's scientific payload included panchromatic and 4-color imagers as well as an imaging spectrometer covering wavelengths from 1.25 to 2.5 µm. Those wavelengths were selected for their sensitivity to Pluto's volatile ices, as well as H₂O and NH₃ ices known to exist on Charon.

The same three volatile species dominate the surface of Neptune's satellite Triton, explored by Voyager II in 1989. Pluto might thus have been expected to host landforms similar to Triton's (though the absence of a nearby giant planet as a source of tidal heating for Pluto is a major difference).

Pluto's geology turned out to hold many surprises, including landscapes not seen on Triton, such as the bladed terrain of Tartarus Dorsa, and cellular and finer-scale patterns in Sputnik Planitia. Likewise, no obvious counterpart to Triton's distinctive cantaloupe terrain was evident on Pluto (although it has been suggested that Triton's cantaloupe terrain might be produced through glacial convection analogous to that in Sputnik Planitia).

Much work has been done investigating the processes responsible for Pluto's distinctive features. The New Horizons instrument suite provided high resolution imaging, including stereo, along with compositional mapping. This talk will show examples where the combination of morphological constraints from imaging with composition from multi-spectral mapping have shed new light on the processes shaping Pluto's surface.

Acknowledgment. This work was supported by NASA's New Horizons project. We thank the New Horizons Science Team, and especially the Geology & Geophysics Science Theme Team, the Surface Composition Science Theme Team, and the Atmospheres Theme Team. Note that feature names in the Pluto system include a mix of formally approved names and informal names.