5. Populations of Planet-Crossing Asteroids and the Relation of Apollo Objects to Main-Belt Asteroids and Comets

Abstract

From discoveries made in several independent surveys of the sky, the number of Apollo asteroids to absolute visual magnitude 18 is estimated to be of the order of 103; the ratio of Mars-crossing asteroids to Apcllos is estimated to lie between 10 and 60. The loss of Apollos to magnitude 18 over the last 3 billion years, by collision with the planets and ejection from the solar system, is estimated to have been several times 104 objects. Mars-crossing asteroids appear to be an inadequate source for all of these objects. Most Apollos probably are dead short-period comets.