ORIGIN OF THE 10-DEGREE SOLAR-SYSTEM DUST BANDS

The Solar System dust bands discovered by IRAS are toroidal distributi ons of dust particles with common proper inclinations. It is impossibl e for particles with high eccentricity (approximately 0.2 or greater) to maintain a near constant proper inclination as they precess, and th erefore the dust bands must be composed of material having a low eccen tricity, pointing to an asteroidal origin. The mechanism of dust band production could involve either a continual comminution of material as sociated with the major Hiray-ama asteroid families, the equilibrium m odel (Dermott et al. (1984) Nature 312, 505-509) or random disruptions in the asteroid belt of small, single asteroids (Sykes and Greenberg (1986) Icarus 65, 51-69). The IRAS observations of the zodiacal cloud from which the dust band profiles are isolated have excellent resoluti on, and the manner in which these profiles change around the sky shoul d allow the origin of the bands, their radial extent, the size-frequen cy distribution of the material and the optical properties of the dust itself to be determined. The equilibrium model of the dust bands sugg ests Eos as the parent of the 10 degrees band pair. Results from detai led numerical modeling of the 10 degrees band pair are presented. It i s demonstrated that a model composed of dust particles having mean sem i-major axis, proper eccentricity and proper inclination equal to thos e of the Eos family member asteroids, but with a dispersion in proper inclination of 2.5 degrees, produces convincing match with observation s. Indeed, it is impossible to reproduce the observed profiles of the 10 degrees band pair without imposing such a dispersion on the dust ba nd material. Since the dust band profiles are matched very well with E os, Themis and Koronis type material alone, the result is taken as str ong evidence in favor of the equilibrium model. The effects of planeta ry perturbations are included by imposing the appropriate forced eleme nts on the dust particle orbits (these forced elements vary with helio centric distance). A subsequent model in which material is allowed to populate the inner solar system by a Poynting-Robertson drag distribut ion is also constructed. A dispersion in proper inclination of 3.5 deg rees provides the best match with observations, but close examination of the model profiles reveals that they are slightly broader than the observed profiles. If the variation of the number density of asteroida l material with heliocentric distance r is given by an expression if t he form 1/r(gamma) then these results indicate that gamma < 1 compared with gamma = 1 expected for a simple Poynting-Robertson drag distribu tion. This implies that asteroidal material is lost from the system as it spirals in towards the Sun, owing to interparticle collisions. (C) 1998 Elsevier Science Ltd. All rights reserved.