The Sublimative Evolution of (486958) Arrokoth

TL;DR

This paper explores Arrokoth's sublimative history, suggesting surface features are recent and shape is primordial, with sublimation playing a limited role in its evolution and current state.

Contribution

It provides a detailed analysis of Arrokoth's sublimative evolution, highlighting the limited impact of sublimation on its rotation and surface features, and proposing a timeline of surface formation.

Findings

Surface features likely formed after sublimative period

Sublimation insufficient to alter Arrokoth's rotation

Surface is not primordial, but shape is primordial

Abstract

We consider the history of New Horizons target (486958) Arrokoth in the context of its sublimative evolution. Shortly after the Sun's protoplanetary disk (PPD) cleared, the newly intense sunlight sparked a sublimative period in Arrokoth's early history that lasted for ~10-100 Myr. Although this sublimation was too weak to significantly alter Arrokoth's spin state, it could drive mass transport around the surface significant enough to erase topographic features on length scales of ~10-100 m. This includes craters up to ~50-500 m in diameter, which suggests that the majority of Arrokoth's craters may not be primordial (dating from the merger of Arrokoth's lobes), but rather could date from after the end of this sublimative period. Thereafter, Arrokoth entered a Quiescent Period (which lasts to the present day), in which volatile production rates are at least 13 orders of magnitude less than the ~10^24 molecules/s detection limit of the New Horizons spacecraft (Lisse et al. 2020). This is insufficient to drive either mass transport or sublimative torques. These results suggest that the observed surface of Arrokoth is not primordial, but rather dates from the Quiescent Period. By contrast, the inability of sublimative torques to meaningfully alter Arrokoth's rotation state suggests that its shape is indeed primordial, and its observed rotation is representative of its spin state after formation.