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Shape, morphology and spin-axis evolution of Planetesimals in the Solar System

Presentation #615.04 in the session Planet Formation Theory.

Published onApr 03, 2024
Shape, morphology and spin-axis evolution of Planetesimals in the Solar System

One of the key findings of the Rosetta mission to the Jupiter family comet 67P/CG was its peculiar bi-lobed shape along with the apparent north/south dichotomy in large scale morphology. This has reignited scientific discussion on the topic of origin, evolution and age of the nucleus. In this work we aim to investigate the role of activity on the overall shape, spin axis, and orbit evolution for comet candidate objects during their ‘storage’ phase in the Kuiper belt. We consider four classes of three-dimensional (3D) shapes for various initial condition of spin-axis and orbital parameters, propagating them for ~109 years. Accounting for solar driven CO ice sublimation (and Knudsen diffusion), we estimate the spin states change and derive upper limits on mass loss distribution on the surface. The results provide argument for activity driven origin of large scale morphology structures, as well as significant alteration of pre-existing landforms due to sublimation. Furthermore, we suggest that the peculiar oblate 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.

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