MAXIMUM VISIBLE POLARIZATION OF 4179 TOUTATIS IN THE APPARITION OF 1996

Our visible polarimetry of asteroid 4179 Toutatis during the apparitio n of 1996 has revealed the existence of a maximum polarization P-max o f (7.0 +/- 0.2)% at a phase angle (Sun-asteroid-observer angle) alpha( max) of 107 degrees +/- 10 degrees at an effective wavelength of 0.53 mu m. This is the second significant report of P-max and alpha(max) fo r 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 P-max and alpha(max) 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 t hose of lunar fines with a size of less than 80 mu m. Furthermore, our multi-channel polarimetry has confirmed a decrease in the polarizatio n with increasing wavelength.