Polarimetry of asteroids

Polarimetric data for 4179 Toutatis were obtained during 23 nights from 10 December 1992 to 29 January 1993 at wavelengths of 0.41, 0.46, 0.54 and 0.70 μm. It is found that: (1) no peak of linear polarization P occurs, at least in our available data, between a phase angle α = 0.3° and 101.3°; (2) the inversion angle, where P = 0, is about 20°; and (3) the polarimetric slope near the inversion angle is about 0.1% deg ^-1. A comparison of our results with published polarimetric data for asteroids has confirmed that 4179 Toutatis is an S-type asteroid. Model calculations of the phase angle dependence of polarization suggest that Toutatis is covered by a coarse regolith on its inhomogeneous rough surfaces.