Low Albedos Among Extinct Comet Candidates

Abstract

We present radiometric effective radii and visual geometric albedos for six asteroids in comet-like orbits. Our sample has three of the four known retrograde asteroids prograde but highly elliptical orbits. These measurements more than double the number of known albedos for asteroids with a Tisserand invariant in the cometary regime. We find that all six of our objects, and nine of the 10 now known, have albedos that are as low as those of active cometary nuclei, which is consistent with their supposed evolutionary connection to that group. This albedo distribution is distinct from that of the whole near-Earth and unusual asteroid population, and the strong correlation between Tisserand invariant and albedo suggests that there is a significant cometary contribution to this asteroid population.