Fast Rotating Asteroids 1999 TY2, 1999 SF10, and 1998 WB2

Abstract An analysis of our photometric observations of near-Earth asteroids 1999 TY 2 , 1999 SF 10 , and 1998 WB 2 has revealed their rotation periods to be 7.2807±0.0003, 2.4663±0.0005, and 18.8±0.3 min, respectively. Their rotations are so fast that the bodies cannot be held together by self-gravitation alone, and must therefore be monoliths. Their absolute magnitudes, 23.1±0.3, 24.0±0.5, and 22.1±0.2, respectively, indicate that they are small bodies with mean diameters in the range 60–120 m. The current statistics of asteroid spin rates vs size suggest that the range where monoliths start to dominate among asteroids is below a diameter of about 200 m, corresponding to H ≈22, as suggested by P. Pravec and A. W. Harris (2000, Icarus, in press).