A STUDY OF HILDA ASTEROIDS - III - COLLISION VELOCITIES AND COLLISIONFREQUENCIES OF HILDA ASTEROIDS

The collision velocities and collision frequencies of Hilda asteroids have been investigated numerically. The collision probabilities and co llision velocities have been determined from a data base of close enco unters, obtained by numerical integrations of the orbits of 909 astero ids for 55000 years; The integration included all known main-belt, Cyb ele, Hilda, and Trojan objects larger than 50 km in diameter. The mean collision probability is lower for Hilda asteroids than for main-belt , Cybele and Trojan asteroids. Out of ten collisions involving a Hilda object, about seven are with main-belt objects, and the other three c ollisions are evenly distributed among the three outer-belt groups. Th e collision probabilities of individual Hilda steroids have a strong c orrelation with the eccentricity of their orbits, resulting in a wide range (about a factor of six) of collision probabilities among the Hil da objects. The mean collision velocity of the Hilda asteroids is 4.6 km s(-1), which is 0.5 km s(-1) lower than the average for main-belt o bjects. The mean collision velocity of individual Hilda objects range from 3.3 to 6.0 km s(-1).