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K. Grogan (NASA Goddard Space Flight Center), S.F. Dermott, T.J.J Kehoe (University of Florida)
The most important dynamical features of the zodiacal cloud are: (i) the dust bands associated with the major Hirayama asteroid families, (ii) the circumsolar ring of asteroidal dust particles in resonant lock with the Earth, (iii) the offset of the center of symmetry of the cloud from the Sun, the tilt of the cloud with respect to the ecliptic, and the warp of the cloud, all produced by secular perturbations, (iv) the radial gradient of the ecliptic polar brightness, determined by the distribution of material at 1 AU.
The dust bands provide the clearest evidence that a substantial and possibly dominant fraction of the cloud originates from asteroids. However, the characteristic diameter of these particle is probably several hundred microns, and the migration of these particles towards the inner Solar System due to Poynting-Robertson light drag and their slow passage through secular resonances at the inner edge of the asteroid belt results in large increases in their eccentricities and inclinations. For this reason, it may be difficult to distinguish clearly between asteroidal and cometary particles in the inner Solar System on dynamical grounds alone.
K.G. acknowledges support by the STIS IDT through NOAO by NASA. This research is supported by NASA PG&G grant NAG5-4531 and ADP grant NAG5-9280.