The effect of the dust size distribution on asteroid polarization

We have developed a theoretical description of how of an asteroid’s polarizationphase curve will be affected by the removal of the dust from the surface due to a sizedependent phenomenon such as radiation pressure-driven escape of levitated particles. We test our calculations against new observations of four small (D ≈ 1 km) nearEarth asteroids [(85236), (142348), (162900) and 2006 SZ217] obtained with the Dual Beam Imaging Polarimeter on the University of Hawaii’s 2.2 m telescope, as well as previous observations of (25143) Itokawa and (433) Eros. We find that the polarization of the light reflected from an asteroid is controlled by the mineralogical and chemical composition of the surface and is independent of dust particle. The relation between the slope of the polarization-phase curve beyond the inversion angle and the albedo of an asteroid is thus independent of the surface regolith size distribution and is valid for both Main Belt and Near-Earth asteroids. Subject headings: Minor planets, asteroids; Polarization