INFRARED ASTRONOMICAL SATELLITE OBSERVATIONS OF ASTEROID DUST BANDS AND COMETARY DUST TRAILS (COLLISIONS, DEBRIS, SOLAR SYSTEM).

Abstract

Analysis of data from the Infrared Astronomical Satellite (IRAS) resulted in the discovery of bands of dust surrounding the inner solar system, consisting of asteroid collision debris (Low et al., 1984). Narrow trails of dust were also discovered tracking the orbits of a number of short-period comets (Sykes et al., 1986). Pairs of dust bands are the product of individual collisional events in the asteroid belt. A dynamical model is developed which shows how the orbits of debris from such collisions evolve to form a band pair. A model of the surface area evolution of such bands is also developed which, coupled with asteroid collision theories, indicates that some of the observed dust bands are the consequence of the disruption of ∼10 km diameter asteroids within the last ∼10⁷ years. Observations of other bands are consistant with more ancient disruptions of much larger asteroids, which resulted in the formation of the Koronis and Themis asteroid families. However, the hypothesis that all dust bands represent the small-particle (∼1 mm) members of the Hirayama families is inconsistent with the IRAS data. Dust particles composing the bands are small enough to have experienced some orbital decay due to Poynting-Robertson drag. From the above models, it is possible to account for the bulk of the zodiacal thermal emission, increasing the importance of asteroid collisions as a source of interplanetary dust. Lower limits on the ages of the major asteroid families are derived. Cometary dust trails consist of particles hundreds of microns and larger in diameter, ejected at low velocities (m/s) from the parent comet, and spreading out ahead and behind the comet's position along its orbital path, the initial stages in the evolution of meteor streams. Dust trails are found in association with short-period comets as diverse as P/Encke (perihelion distance, q = .33 AU) and P/Schwassmann-Wachmann 1 (q = 5.43 AU). Analysis of dust trails indicates possible differences in structure and composition among comet nuclei. Preliminary results from a survey of dust trails in the IRAS data indicate the presence of a large number of previously unobserved short-period comets.