The location of Pluto’s large glacier, Sputnik Planitia, can be explained as an impact basin which reoriented via true polar wander as it loaded with ice. We use a coupled true polar wander and climate model to analyze how these two processes work together to place Sputnik at its present-day location. The model is constrained by the final location of Sputnik Planitia (17.7°N, 178.2°E) and the observed 2 km elevation difference between the top of the ice in the glacier and the level of the rest of the surface. We find that true polar wander coupled with atmospheric condensation is a viable mechanism for the formation and present-day location of Sputnik Planitia, even when accounting for Pluto’s orbital obliquity cycle and the flexural response of the underlying crust. The initial impact basin could have formed north or northwest of the present-day location, at latitudes between 35°N and 50°N. The mean thickness of N2 in the final glacier is constrained by the model to be at most 2 km. Larger amounts of N2 ice reorient too close to the anti-Charon point (0°N, 180°E). The empty basin is constrained by the model to be 2.5 to 3 km deep initially, although the crust flexes downwards by 0.5 km for every 1 km of N2 ice that condenses into the basin, so the present-day depth is expected to be 3 to 4 km. After reaching the final location, the glacier undergoes short periods of sublimation and re-condensation on the order of ten meters of ice, due Pluto’s variable obliquity cycle, which drives short periods of reorientation of a few km. The obliquity cycle also has a role in the onset of glacial infilling; some initial basin locations are only able to begin accumulating N2 ice at certain points during the obliquity cycle. We also explore the sensitivity of the coupled model to surface albedo and initial obliquity. At the time of the impact and subsequent infilling of the basin, Pluto may have been on a different orbit, so we explore the effect of a different semi-major axis on the glacier formation as well.
This work has been submitted for publication: Johnson, Keane, Young, and Matsuyama, New Constraints on Pluto’s Sputnik Planitia Glacier from a Coupled Reorientation-Climate Model, PSJ, submitted 2021