Albedos of Small Hilda Group Asteroids as Revealed by Spitzer

TL;DR

This study uses Spitzer 24 μm data to measure the albedos of 62 small Hilda asteroids, revealing a higher and more varied albedo distribution compared to larger members, with implications for their composition and origin.

Contribution

First thermal infrared measurements of small Hilda asteroids, providing new albedo data and insights into their size distribution and compositional diversity.

Findings

Small Hilda asteroids have a mean albedo of 0.07, higher than larger ones.

Small Hildas show a broader albedo range, indicating diverse compositions.

Results support theories of outer solar system material migration into the asteroid group.

Abstract

We present thermal 24 $\mu$m observations from the \textit{Spitzer Space Telescope} of 62 Hilda asteroid group members with diameters ranging from 3 to 12 kilometers. Measurements of the thermal emission when combined with reported absolute magnitudes allow us to constrain the albedo and diameter of each object. From our \textit{Spitzer} sample, we find the mean geometric albedo, $p_{V} =$ 0.07 $\pm$ 0.05 for small (D $<$ 10 km) Hilda group asteroids. This value of $p_{V}$ is greater than and spans a larger range in albedo space than the mean albedo of large (D $\gtrsim$ 10 km) Hilda group asteroids which is $p_{V} =$ 0.04 $\pm$ 0.01. Though this difference may be attributed to space weathering, the small Hilda group population reportedly displays greater taxonomic range from C-, D- and X-type whose albedo distributions are commensurate with the range of determined albedos. We discuss the derived Hilda size-frequency distribution, color-color space, and geometric albedo for our survey sample in the context of the expected migration induced "seeding" of the Hilda asteroid group with outer solar system proto-planetesimals as outlined in the "Nice" formalism.