Physical Properties of Kuiper Belt and Centaur Objects: Constraints from Spitzer Space Telescope

TL;DR

This study uses Spitzer Space Telescope data to analyze the physical properties of Kuiper Belt and Centaur objects, revealing correlations between albedo, size, perihelion distance, and color, and providing insights into their composition and evolution.

Contribution

The paper presents a comprehensive analysis of 47 KBOs and Centaurs using thermal modeling, identifying new correlations between albedo, size, perihelion, and color, and summarizing existing measurements.

Findings

Albedos of KBOs and Centaurs are correlated with perihelion distance.

Larger KBOs tend to have higher albedos.

The three or four largest KBOs have distinct albedo characteristics.

Abstract

Detecting heat from minor planets in the outer solar system is challenging, yet it is the most efficient means for constraining the albedos and sizes of Kuiper Belt Objects (KBOs) and their progeny, the Centaur objects. These physical parameters are critical, e.g., for interpreting spectroscopic data, deriving densities from the masses of binary systems, and predicting occultation tracks. Here we summarize Spitzer Space Telescope observations of 47 KBOs and Centaurs at wavelengths near 24 and 70 microns. We interpret the measurements using a variation of the Standard Thermal Model (STM) to derive the physical properties (albedo and diameter) of the targets. We also summarize the results of other efforts to measure the albedos and sizes of KBOs and Centaurs. The three or four largest KBOs appear to constitute a distinct class in terms of their albedos. From our Spitzer results, we find that the geometric albedo of KBOs and Centaurs is correlated with perihelion distance (darker objects having smaller perihelia), and that the albedos of KBOs (but not Centaurs) are correlated with size (larger KBOs having higher albedos). We also find hints that albedo may be correlated with with visible color (for Centaurs). Interestingly, if the color correlation is real, redder Centaurs appear to have higher albedos. Finally, we briefly discuss the prospects for future thermal observations of these primitive outer solar system objects.