# Col-OSSOS: Color and Inclination are Correlated Throughout the Kuiper Belt

## TL;DR

This study reveals a correlation between color and inclination in Trans-Neptunian Objects, showing that red objects tend to have lower inclinations than gray ones, indicating different formation locations in the early Solar System.

## Contribution

It provides high-precision color measurements for 25 TNOs and demonstrates a statistically significant correlation between color class and orbital inclination across the entire population.

## Key findings

- Red TNOs have lower inclinations than gray TNOs.
- Color bimodality is intrinsic and not due to observational biases.
- Supports the idea of different formation regions in the early Solar System.

## Abstract

Both physical and dynamical properties must be considered to constrain the origins of the dynamically excited distant Solar System populations. We present high-precision (g-r) colors for 25 small (Hr>5) dynamically excited Trans-Neptunian Objects (TNOs) and centaurs acquired as part of the Colours of the Outer Solar System Origins Survey (Col-OSSOS). We combine our dataset with previously published measurements and consider a set of 229 colors of outer Solar System objects on dynamically excited orbits. The overall color distribution is bimodal and can be decomposed into two distinct classes, termed `gray' and `red', that each has a normal color distribution. The two color classes have different inclination distributions: red objects have lower inclinations than the gray ones. This trend holds for all dynamically excited TNO populations. Even in the worst-case scenario, biases in the discovery surveys cannot account for this trend: it is intrinsic to the TNO population. Considering that TNOs are the precursors of centaurs, and that their inclinations are roughly preserved as they become centaurs, our finding solves the conundrum of centaurs being the only outer Solar System population identified so far to exhibit this property (Tegler et al. 2016). The different orbital distributions of the gray and red dynamically excited TNOs provide strong evidence that their colors are due to different formation locations in a disk of planetesimals with a compositional gradient.