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Constraints on the Formation of Classical KBOs from the Shape of Arrokoth

Presentation #209.01 in the session TNO Theory/Formation and Observational Surveys (Oral Presentation)

Published onOct 23, 2023
Constraints on the Formation of Classical KBOs from the Shape of Arrokoth

The cold classical KBO (486958) Arrokoth is the only classical KBO to have been visited by a spacecraft, NASA’s New Horizons in January 2019. Arrokoth is formed from two separate lobes, the larger lenticular lobe “Wenu” and a smaller, more spherical lobe “Weeyo”. The very narrow contact point between the lobes implies that they were fully formed separately and later merged to form the final contact binary. This formation story is consistent with their rapid formation by the Streaming Instability (SI) from the same cloud of material and later slow, non-violent contact. In this work, we use the newly updated and improved shape mode of Arrokoth to explore how the shapes of Wenu and Weeyo constrain both the formation of Arrokoth, and of other, similar KBOs. This is particularly important given the binary and contact-binary rates are comparably high in the Kuiper Belt, and the true rate of contact binaries could be much higher than photometric surveys suggest. We look how well the lobes are aligned to each other, a critical test of the speed of their contact. We explore the apparent hexagonal shape of Wenu, which constrains its formation. We also address separated binary classical KBOs, which are likely to have similar shapes to the lobes of Arrokoth, and how the large J2 of an object like Wenu can modify the orbital evolution of a binary KBO.

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