High Albedos of Low Inclination Classical Kuiper Belt Objects

TL;DR

This study uses Spitzer observations to determine that cold Classical Kuiper Belt Objects have higher albedos than other TNOs, impacting mass estimates and revealing diversity in surface properties.

Contribution

It provides new thermal emission measurements for 15 TNOs, especially cold Classical KBOs, showing their higher albedos and reducing the estimated mass of the cold Classical Kuiper Belt.

Findings

Cold Classical TNOs have higher albedos than hot Classicals.

The mass of the cold Classical Kuiper Belt is significantly lower than previous estimates.

Diversity in albedos suggests complex surface properties unrelated to color.

Abstract

We present observations of thermal emission from fifteen transneptunian objects (TNOs) made using the Spitzer Space Telescope. Thirteen of the targets are members of the Classical population: six dynamically hot Classicals, five dynamically cold Classicals, and two dynamically cold inner Classical Kuiper Belt Objects (KBOs). We fit our observations using thermal models to determine the sizes and albedos of our targets finding that the cold Classical TNOs have distinctly higher visual albedos than the hot Classicals and other TNO dynamical classes. The cold Classicals are known to be distinct from other TNOs in terms of their color distribution, size distribution, and binarity fraction. The Classical objects in our sample all have red colors yet they show a diversity of albedos which suggests that there is not a simple relationship between albedo and color. As a consequence of high albedos, the mass estimate of the cold Classical Kuiper Belt is reduced from approximately 0.01 Earth masses to approximately 0.001 Earth masses. Our results also increase significantly the sample of small Classical KBOs with known albedos and sizes from 21 to 32 such objects.