THE 3-DIMENSIONAL STRUCTURE OF THE ZODIACAL DUST BANDS

Using observations of the infrared sky brightness by the Cosmic Backgr ound Explorer (COBE)(1) Diffuse Infrared Background Experiment (DIRBE) and Infrared Astronomical Satellite (IRAS), we have created maps of t he surface brightness Fourier-filtered to suppress the smallest (< 1 d egrees) structures and the large-scale background (>15 degrees). Dust bands associated with the Themis, Koronis, and Eos families are readil y evident. A dust band associated with the Maria family is also presen t, The parallactic distances to the emitting regions of the Koronis, E os, and Maria dust bands were found to be 1.4 to 2.5 AU, A weak dust b and associated with the Eunomia/Io family is evident, together with an other weak and previously unattributed dust band, which may split furt her into two band pairs, potentially associated with the Hygiea or Ves ta family, The brightnesses of the blended Themis/Koronis bands and th e Eos dust band vary with ecliptic longitude, such that the northern o r southern component of the band pair becomes brighter when its tilt b rings it into the ecliptic plane. We attribute the brightness variatio ns to the motion of the Earth within the emitting region, and conclude that at least some dust-band particles are on Earth-crossing orbits. For the Themis and Koronis families, the tilt is sufficient that the E arth may pass to the edges of the emitting region, where the density i s highest, leading to ''glints'' two or four times a year, We compared the observed distributions to theoretically motivated, empirical mode ls for the three-dimensional distribution of asteroid family dust. In the torus model, the dust is distributed among the asteroid family mem bers with the same distributions of proper orbital inclination and sem imajor axis but a random ascending node. In the migrating model, parti cles are presumed to be under the influence of Poynting-Robertson drag , so that they are distributed throughout the inner Solar System. The migrating model is better able to match the parallactic variation of d ust-band latitude as well as the 12- to 60-mu m spectrum of the dust b ands. The annual brightness variations can be explained only by the mi grating model. Upper limits are placed on the dust density associated with the Nysa and Flora families-both of the large, inner-belt familie s with wide inclination dispersions, The association of five (and pote ntially seven) dust bands with the largest asteroid families suggests that dust bands are an integral part of asteroid families, If nonfamil y asteroids produce dust at a rate similar to that of the families wit h the lowest dust density, then they can account for the brightness of the zodiacal light in the ecliptic. (C) 1997 Academic Press.