Col-OSSOS: Evidence for a compositional gradient inherited from the protoplanetary disk?

TL;DR

This study suggests a compositional gradient in the early protoplanetary disk, inferred from correlations between TNO orbital inclinations and colors, indicating a link between formation location and composition in the Kuiper Belt.

Contribution

It provides evidence for a compositional gradient inherited from the protoplanetary disk based on orbital and color data of TNOs, supported by numerical simulations.

Findings

BrightIR TNOs' inclinations correlate with their colors.

Simulation results suggest a formation location gradient in the early disk.

Uncertainties remain due to blue contaminants and alternative explanations.

Abstract

In the present-day Kuiper Belt, the number of compositional classes and the orbital distributions of these classes hold important cosmogonic implications for the Solar System. In a companion paper by Fraser et al., we demonstrate that the observed color distribution of small (H>6) Trans-Neptunian Objects (TNOs) can be accounted for by the existence of only two composition classes, named brightIR and faintIR, where the range of colors in each class is governed by a mixture of two material end members. Here, we investigate the orbital distribution of the two color classes identified by Fraser et al. and find that the orbital inclinations of the brightIR class objects are correlated with their optical colors. Using the output of numerical simulations investigating the orbital evolution of TNOs during their scattering phase with Neptune, we show that this correlation could reflect a composition gradient in the early protoplanetary disk, in the range of heliocentric distances over which TNOs from the brightIR class accreted. However, tensions between this interpretation and the existence of blue contaminants among cold classical TNOs, and possible alternative origins for the detected correlation, currently bear uncertainty on our proposed interpretation.