The Hubble Wide Field Camera 3 Test of Surfaces in the Outer Solar System: The Compositional Classes of the Kuiper Belt

TL;DR

This study uses Hubble WFC3 data to analyze surface compositions of Kuiper belt objects, revealing two main compositional classes with bifurcated color distributions, suggesting primordial origins and evolutionary processes affecting larger objects.

Contribution

First comprehensive survey linking surface properties of Kuiper belt objects with their dynamical classes, identifying two distinct compositional groups and evolutionary implications.

Findings

Centaurs and scattered disk objects show bifurcated color distributions.

Small excited objects follow the mixing model, indicating primordial bifurcation.

Large objects deviate from the model, implying evolutionary processes.

Abstract

We present the first results of the Hubble Wide Field Camera 3 Test of Surfaces in the Outer Solar System (H/WTSOSS). The purpose of this survey was to measure the surface properties of a large number of Kuiper belt objects and attempt to infer compositional and dynamical correlations. We find that the Centaurs and the low-perihelion scattered disk and resonant objects exhibit virtually identical bifurcated optical colour distributions and make up two well defined groups of object. Both groups have highly correlated optical and NIR colours which are well described by a pair of two component mixture models that have different red components, but share a common neutral component. The small, $H_{606}\gtrsim5.6$ high-perihelion excited objects are entirely consistent with being drawn from the two branches of the mixing model suggesting that the colour bifurcation of the Centaurs is apparent in all small excited objects. On the other hand, objects larger than $H_{606}\sim5.6$ are not consistent with the mixing model, suggesting some evolutionary process avoided by the smaller objects. The existence of a bifurcation amongst all excited populations argues that the two separate classes of object existed in the primordial disk before the excited Kuiper belt was populated. The cold classical objects exhibit a different type of surface which has colours that are consistent with being drawn from the red branch of the mixing model, but with much higher albedos.