Colors of Inner Disk Classical Kuiper Belt Objects

TL;DR

This study presents new optical color measurements of inner classical Kuiper Belt objects, revealing a mixture of neutral and red objects and differences from other Kuiper Belt populations, which may indicate compositional or evolutionary distinctions.

Contribution

It provides the first detailed color analysis of inner classical Kuiper Belt objects, highlighting their distinct color distribution compared to other Kuiper Belt populations.

Findings

Inner belt objects form neutral and reddish color groups.

No significant color difference between inner belt objects and Centaurs, plutinos, or scattered disk objects.

Inner belt objects differ in color from cold classical Kuiper Belt objects.

Abstract

We present new optical broadband colors, obtained with the Keck 1 and Vatican Advanced Technology telescopes, for six objects in the inner classical Kuiper Belt. Objects in the inner classical Kuiper Belt are of interest as they may represent the surviving members of the primordial Kuiper Belt that formed interior to the current position of the 3:2 resonance with Neptune, the current position of the plutinos, or, alternatively, they may be objects formed at a different heliocentric distance that were then moved to their present locations. The six new colors, combined with four previously published, show that the 10 inner belt objects with known colors form a neutral clump and a reddish clump in B-R color. Nonparametric statistical tests show no significant difference between the B-R color distribution of the inner disk objects compared to the color distributions of Centaurs, plutinos, or scattered disk objects. However, the B-R color distribution of the inner classical Kuiper belt objects does differ significantly from the distribution of colors in the cold (low inclination) main classical Kuiper belt. The cold main classical objects are predominately red, while the inner classical belt objects are a mixture of neutral and red. The color difference may reveal the existence of a gradient in the composition and /or surface processing history in the primordial Kuiper Belt, or indicate that the inner disk objects are not dynamically analogous to the cold main classical belt objects.