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Abstract

The New Horizons spacecraft’s flyby of Kuiper belt object (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°). 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 Kuiper belt objects and potentially their dynamically derived objects, Centaurs and Jupiter-family comets. 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 1–100 Myr, while its spin state would not be dramatically affected. We further argue that such a process may be ubiquitous in the evolution of the shape of Kuiper belt objects shortly after their formation. This shape-changing process could also be reactivated when Kuiper belt objects dynamically evolve to become Centaurs and then Jupiter-family comets and receive markedly increased solar heating.