The impact of IRAS on asteroidal science

Abstract

Asteroids are studied because, together with comets, they are one of the few sources of information on conditions in the early solar system. Asteroids have been classified into a small number of distinct types and the distribution of these types with respect to their distances from the sun gives information on the chemical structure of the primitive solar nebula. Asteroids are also believed to be the primary source of meteorites and thus the most abundant, diverse and accessible source of extraterrestrial material. There have been several major advances in asteroidal science in recent years. We now have a clear understanding of the origin of some of the Kirkwood gaps in the distribution of asteroidal semimajor axes and of the role that these gaps have in the delivery of meteorites to the Earth. Secondly, the number of meteorites available for study has increased since the discovery of the meteorite fields on the Antarctic ice cap. As expected, IRAS data on asteroidal albedos (the diameters and albedos of 1,811 asteroids have now been measured) will vastly extend the classification work. We anticipate that new insights into the chemical structure of the asteroid belt will be revealed by plotting the variations of the colors and albedos of asteroids in a given class against their distance from the sun. Unexpected products of the IRAS mission include the discovery of a small body in the Geminid meteor stream and the discovery of structure in the zodiacal cloud. The IRAS solar system dust bands provide a further connection with asteroids since they may be collision products of asteroids, possibly members of the major Hirayama families, implying that asteroids may be a significant source of the particles in the zodiacal cloud.