A Possible Divot in the Size Distribution of the Kuiper Belt's Scattering Objects

TL;DR

This paper identifies a divot in the size distribution of Kuiper Belt scattering objects, suggesting a relic of planetesimal formation and providing insights into their orbital and size characteristics.

Contribution

It introduces evidence for a divot in the size distribution of Kuiper Belt objects, challenging single power-law models and linking formation history to current orbital properties.

Findings

A divot in the size distribution below 100 km diameter.

The size distribution supports a collisional equilibrium for smaller objects.

Scattering objects' inclination distribution implies a pre-heated source region.

Abstract

Via joint analysis of a calibrated telescopic survey, which found scattering Kuiper Belt objects, and models of their expected orbital distribution, we measure the form of the scattering object's size distribution. Ruling out a single power-law at greater than 99% confidence, we constrain the form of the size distribution and find that, surprisingly, our analysis favours a very sudden decrease (a divot) in the number distribution as diameters decrease below 100 km, with the number of smaller objects then rising again as expected via collisional equilibrium. Extrapolating at this collisional equilibrium slope produced enough kilometer-scale scattering objects to supply the nearby Jupiter-Family comets. Our interpretation is that this divot feature is a preserved relic of the size distribution made by planetesimal formation, now "frozen in" to portions of the Kuiper Belt sharing a "hot" orbital inclination distribution, explaining several puzzles in Kuiper Belt science. Additionally, we show that to match today's scattering-object inclination distribution, the supply source that was scattered outward must have already been vertically heated to of order 10 degrees.