ROAMING THE HILLS AND VALLEYS OF THE SOLAR SYSTEM: TOPOGRAPHIC MAPPING FROM THE MOON TO PLUTO (AND BEYOND)

Stereo imaging and topographic mapping of geologic surfaces have been key tools in geologic studies beginning with the first aerial photography of Earth in the early 20^th century. This tradition continued into the Space Age when remote sensing (i.e., imaging) had to suffice for field work. The authors, along with others, have been consistent advocates for several decades for planetary stereo imaging as a geologic mapping aid and for generating topographic maps (DEMs). This collaboration first bore fruit when Viking stereo images were successfully used to map topography of Mars’ south polar cap and terrains prior to acquisition of MGS altimetry. Voyager data were used to map landslides on Io (from which a compressional origin of its many mountains originates), “volcanic plains” on Ganymede, and deformation on mid-sized icy satellites from Tethys to Miranda. Stereo images (in extremely limited quantities) became important for the interpretation of high-Sun Galileo images of the Galilean satellites; followed by Cassini’s first global detailed topographic mapping of mid-sized icy moons. It was also quickly realized during planning how important stereo and stereo topography would be when New Horizons arrived at Pluto in July 2015. Pluto did not disappoint: towering mountains of water ice 2-6 km high and troughs several km deep were observed over the ~40% of Pluto so mapped. Similarly, with 18+km of relief, Pluto’s icy moon Charon has some of the deepest relief on any mid-sized icy moon, including fault-bounded troughs 3-5 km deep. Stereogrammetric mapping of Ceres has also been key for mapping of bright carbonate deposits and impact-related structures. Stereo will continue to be vital to planetary mapping, including New Horizons mapping of the KBO “Ultima Thule,” and upcoming Discovery missions to Psyche and the Trojan asteroids. Stereo will also be key for understanding the surface of Europa during low-altitude mapping and using Lander surface images in the near future.