OSSOS II: A Sharp Transition in the Absolute Magnitude Distribution of the Kuiper Belt's Scattering Population

TL;DR

This study reveals a transition in the size distribution of scattering Trans-Neptunian Objects, favoring a divot model over a single-slope, which has implications for understanding Kuiper Belt formation and the source of Jupiter-Family Comets.

Contribution

It provides the first evidence of a divot in the absolute magnitude distribution of scattering TNOs, supported by multiple surveys and independent of formation models.

Findings

The H-distribution shows a transition around H_g ~ 9.

A divot distribution explains multiple Kuiper Belt populations.

Estimated scattering TNOs number (2.4-8.3)×10^5 for H_r < 12.

Abstract

We measure the absolute magnitude, $H$, distribution, $dN(H) \propto 10^{\alpha H}$ of the scattering Trans-Neptunian Objects (TNOs) as a proxy for their size-frequency distribution. We show that the H-distribution of the scattering TNOs is not consistent with a single-slope distribution, but must transition around $H_g \sim 9$ to either a knee with a shallow slope or to a divot, which is a differential drop followed by second exponential distribution. Our analysis is based on a sample of 22 scattering TNOs drawn from three different TNO surveys, the Canada-France Ecliptic Plane Survey (CFEPS, Petit et al. 2011), Alexandersen et al. (2014), and the Outer Solar System Origins Survey (OSSOS, Bannister et al. 2016), all of which provide well characterized detection thresholds, combined with a cosmogonic model for the formation of the scattering TNO population. Our measured absolute magnitude distribution result is independent of the choice of cosmogonic model. Based on our analysis, we estimate that number of scattering TNOs is (2.4-8.3)$\times 10^5$ for $H_r < 12$. A divot $H$-distribution is seen in a variety of formation scenarios and may explain several puzzles in Kuiper Belt science. We find that a divot $H$-distribution simultaneously explains the observed scattering TNO, Neptune Trojan, Plutino, and Centaur $H$-distributions while simultaneously predicting a large enough scattering TNO population to act as the sole supply of the Jupiter-Family Comets.