ALBEDOS OF SMALL HILDA GROUP ASTEROIDS AS REVEALED BY SPITZER

We present thermal 24 μm observations from the Spitzer Space Telescope of 62 Hilda asteroid group members with diameters ranging from 3 to 12 km. Measurements of the thermal emission, when combined with reported absolute magnitudes, allow us to constrain the albedo and diameter of each object. From our Spitzer sample, we find the mean geometric albedo, pV = 0.07 ± 0.05, for small (D < 10 km) Hilda group asteroids. This Spitzer-derived value of pV is greater than and spans a larger range in albedo space than the mean albedo of large (D ∼> 10 km) Hilda group asteroids which is pV = 0.04 ± 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.