Sublimation as an effective mechanism for flattened lobes of (486958) Arrokoth

TL;DR

This paper proposes that sublimation-driven volatile outgassing can explain the flattened, bilobed shape of Kuiper Belt Object Arrokoth, suggesting shape evolution occurs early and may recur during its transition to Centaurs and JFCs.

Contribution

The study introduces a mass loss driven shape evolution model (MONET) demonstrating sublimation as a key mechanism for KBO shape changes, supported by Arrokoth's observed features.

Findings

Arrokoth's shape likely evolved from sublimation processes.

Shape change timescale estimated between 1 to 100 million years.

Sublimation-driven shape evolution may be common among KBOs.

Abstract

The New Horizons spacecraft's flyby of Kuiper Belt Object (KBO) (486958) Arrokoth revealed a bilobed shape with highly flattened lobes both aligned to its equatorial plane, and a rotational axis almost aligned to the orbital plane (obliquity ~99 deg). Arrokoth belongs to the Cold Classical Kuiper Belt Object population that occupies dynamically undisturbed orbits around the Sun, and as such, is a primitive object that formed in situ. Therefore, whether its shape is primordial or evolutionary carries important implications for understanding the evolution of both KBOs and potentially their dynamically derived objects, Centaurs and Jupiter Family Comets (JFC). Applying our mass loss driven shape evolution model (MONET), here we suggest that the current shape of Arrokoth could be of evolutionary origin due to volatile outgassing in a timescale of about 1 to 100 Myr, while its spin state would not significantly affected. We further argue that such a process may be ubiquitous in the evolution of the shape of KBOs shortly after their formation. This shape changing process could also be reactivated when KBOs dynamically evolve to become Centaurs and then JFCs and receive dramatically increased solar heating.