High-resolution Topography of Pluto: Insights into Sputnik Planitia Basin and Ice Sheet

The prominent Sputnik Planitia (SP) basin is likely an ancient impact scar modified by subsequent erosion and infill of N2 and other volatile ices. Here we reeexamine the observational constraints on the formation of these features using controlled topographic data updated from framing camera only data and a revised Pluto pole position. To avoid geometric distortions inherent in line-scan imaging we use LORRI and 5 framing mode MVIC images to produce a coarse elevation map of the encounter hemisphere of Pluto from camera vector bundle adjustments using match points linking >3 images. These match point radius solutions are variable in quality with the best parallax being along the three LORRI image strips near closest approach. These image strips were then used to produce full-resolution stereo and photoclinometric DEMs along those tracks. The interior of SP ice sheet was more problematic due to the small scale and changing photometric behavior of features within it, resulting in noisy DEMs with data gaps. Despite this, it is evident that the ice sheet is level in elevation to within ~200 m except a gradual downward slope north of ~35N where long-term sublimation erosion of ices is expected. Although the depth relative to the rim remains 2-3 km, the absolute elevation of the ice sheet with respect to the mean planetary surface remains unclear (as of this writing) due to the large size of the SP depression and possible distortion on the resulting maps, and differences in elevation around SP. The western flank slopes gradually upward ~1 km toward the eroded rim, but the northeastern flank more downward toward the rim in that quadrant (which also corresponds to a heavily pitted terrain), suggesting a fundamental difference in terrains on the leading and trailing hemispheres. The southeast flank corresponds to a broad glacially eroded plateau ~1 km above mean and coated with bright frosts (east Tombaugh Regio). These data suggest the surface of the ice sheet is ~1.5 km below the hemispheric mean but may be uncertain by ~0.5 km. The depth of the basin floor beneath the ice sheet is not known but could be several kilometers. Further analysis will yield relief across convection cells and small surficial pits across the ice sheet reported at the meeting.