Maximum visible polarization of 4179 Toutatis in the apparition of 1996

Abstract

Our visible polarimetry of asteroid 4179 Toutatis during the apparition of 1996 has revealed the existence of a maximum polarization Pmax of (7.0 ± 0.2)% at a phase angle (Sun-asteroid-observer angle) αmax of 107° ± 10° at an effective wavelength of 0.53 μm. This is the second significant report of Pmax and αmax for the asteroids; the first one for 1685 Toro by Kiselev et al. (1990, AAA51.098.084) has large uncertainties. A comparison of our values of Pmax and αmax with those of laboratory measurements reported by Bowell et al. (1972, Proc. Lunar Sci. Conf.) as well as Shkuratov and Opanasenko (1992, AAA56.094.027) suggests that the Toutatis' surface is covered with a material having similar polarimetric properties to those of lunar fines with a size of less than 80 μm. Furthermore, our multi-channel polarimetry has confirmed a decrease in the polarization with increasing wavelength.