PLUTO FOLLOWED ITS HEART: REORIENTATION AND FAULTING OF PLUTO DUE TO VOLATILE LOADING IN SPUTNIK PLANUM

The New Horizons flyby revealed Pluto to be a wonderfully diverse, geologically active world. The single largest (and most unexpected) feature on the New Horizons encounter hemisphere is Sputnik Planum—a 1000 km diameter probable impact basin filled with several kilometers of actively convecting volatile ices (N₂, CH₄, CO). Curiously, Sputnik Planum is located very near to the anti-Charon point, along the Pluto-Charon tidal axis. The alignment of of large geologic features with principal axes of inertia (such as the tidal axis) is the hallmark of true polar wander. In this work, we show that loading of several kilometers of volatile ice within the Sputnik Planum basin can significantly alter Pluto’s moments of inertia, and result in nearly 60° of reorientation of the body with respect to the spin/tidal axes. As a planet undergoes polar wander, each location on the surface experiences a change in tidal/centrifugal potential, resulting in the accumulation of stress. These reorientation stresses—coupled with stresses due to volatile loading and global expansion of Pluto due to the freezing of a subsurface ocean—produce a global network of extensional faults that closely match the observed distribution of faults on Pluto. We hypothesize that Sputnik Planum formed northwest of its present location and that it was subsequently filled with ice due to seasonal and secular volatile transport cycles. Pluto’s past, present, and future orientation is controlled by complicated feedbacks between volatile transport, changing insolation conditions, and Pluto’s interior structure. Similar volatile-induced reorientation events may occur on other cold, icy moons and Kuiper belt objects.