How Fast did Pluto’s Sputnik Basin Fill? Infilling Timescales for Multiple Initial Locations and Orbits

Surface depressions are natural cold traps for volatiles, due to the increased atmospheric pressure at their surfaces relative to the surrounding terrain. Infilling of depressions can create mass anomalies that affect the body’s moments of inertia. The largest depression on Pluto, Sputnik Planitia, is proposed to be as deep as 10 km and is partially filled by a 3 to 7 km thick nitrogen-methane ice glacier. Loading of volatile ices into the Sputnik Planitia basin is thought to have contributed to a true polar wander reorientation of Pluto (Keane et al. 2016). Atmospheric volatiles preferentially condense into the basin, and the rate of infill depends on the initial latitude and depth of the basin, as well as Pluto’s orbit at the time of basin formation and infill. The initial latitude controls the solar insolation onto the basin, and the depth determines how much easier it is for volatile gases to condense into the depression relative to the surrounding terrain, both of which contribute to the energy balance at the basin floor compared to the ices elsewhere on Pluto. Additionally, the orbital obliquity affects which latitudes on Pluto receive the least orbit-averaged insolation. We calculate infilling timescales for various initial latitudes, depths, and orbits, to better inform true polar wander models and to understand under what conditions a Sputnik Planitia-like ice sheet will form and survive on Pluto. In this presentation, we will discuss the dependence of the infilling timescale on basin and orbit parameters. This work was funded in part by NASA ROSES SSW grants NNX15AH35G and 80NSSC20K0819.