Main Belt Asteroids with WISE/NEOWISE: Near-Infrared Albedos

TL;DR

This study provides revised near-infrared albedo measurements for 2835 Main Belt asteroids using WISE/NEOWISE data, revealing distinct reflectance groups and their relation to asteroid taxonomy and families.

Contribution

It introduces a method for deriving more accurate near-infrared albedos from simultaneous reflected-light and thermal measurements, enhancing asteroid classification.

Findings

Main Belt asteroids separate into three reflectance groups at 3.4 um.

Asteroid families show narrow albedo distributions within these groups.

Near-infrared albedos are useful for asteroid taxonomy and identifying targets for follow-up.

Abstract

We present revised near-infrared albedo fits of 2835 Main Belt asteroids observed by WISE/NEOWISE over the course of its fully cryogenic survey in 2010. These fits are derived from reflected-light near-infrared images taken simultaneously with thermal emission measurements, allowing for more accurate measurements of the near-infrared albedos than is possible for visible albedo measurements. As our sample requires reflected light measurements, it undersamples small, low albedo asteroids, as well as those with blue spectral slopes across the wavelengths investigated. We find that the Main Belt separates into three distinct groups of 6%, 16%, and 40% reflectance at 3.4 um. Conversely, the 4.6 um albedo distribution spans the full range of possible values with no clear grouping. Asteroid families show a narrow distribution of 3.4 um albedos within each family that map to one of the three observed groupings, with the (221) Eos family being the sole family associated with the 16% reflectance 3.4 um albedo group. We show that near-infrared albedos derived from simultaneous thermal emission and reflected light measurements are an important indicator of asteroid taxonomy and can identify interesting targets for spectroscopic followup.