ASTEROIDS FALLING INTO THE SUN

THE orbits of comets and near-Earth asteroids evolve chaotically, main ly in response to the gravitational influence of the planets. For come ts, it is known that such perturbations can result in trajectories tha t either collide with or graze the Sun(1-3). Indeed, it has been calcu lated(3) that 6% of the known short-period comets (including comet Enc ke) will become Sun-grazers an a timescale of similar to 10(5) years. But there has been no previous indication that asteroids may suffer a similar fate. To address this question, we have integrated numerically the orbits of several near-Earth asteroids. We find that these astero ids can also undergo solar collisions, through several dynamical route s involving orbital resonances with the giant planets, on timescales o f the order of 10(6) years. Of the 47 objects studied, we found 19 cas es in which the asteroid collided with the Sun, implying that solar co llisions are a more common fate than planetary collisions or ejection from the Solar System. Past Sun-grazing events may also have been reco rded in the surface composition and spectral properties of some existi ng near-Earth asteroids.