Opposition effect of asteroids

The opposition effect behavior is analyzed for 33 asteroids with well-measu red magnitude-phase curves. It is shown that surface albedo is the main fac tor influencing the amplitude and width of the asteroid opposition effect. The amplitude of opposition effect depends on asteroid albedo in a non-mono tonic way with the maximum for moderate albedo asteroids decreasing both fo r dark and for high albedo asteroids. This can be explained by the combined influence of both shadow hiding and coherent-backscatter mechanisms. The r elative contribution of the coherent-backscatter effect to the asteroid mag nitude-phase dependence close to opposition (alpha = 0.3 degrees) is estima ted to be about 20-60% for low albedo asteroids and 80-90% for high and mod erate albedo asteroids. At alpha > 5 degrees the shadow-hiding effect has t he dominant influence. A tendency was found for asteroids with larger U-B c olors to show larger values of the opposition effect. We also compare the o pposition effects of asteroids with those of some atmosphereless satellites and meteorites. (C) 2000 Academic Press.