Discussion of paper by S. J. Peale, ‘Dust belt of the Earth’

In a recent paper, Peale [1966] has suggested that part, or indeed all, of the zodiacal light could be due to dust particles in geocentric orbits rather than in heliocentric orbits as is generally believed. Such particles are subject to gravitational perturbations due to the earth's oblateness and the presence of the sun and moon, as well as to the effects of radiation pressure. Peale [1966] argues that radiation pressure will produce a diffuse concentration of dust particles near the ecliptic plane and that the asymmetry with respect to the ecliptic will be almost completely undisturbed by the gravitational perturbations beyond a geocentric distance of 7.7 earth radii, where the effects of oblateness and lunisolar forces are equal. On the other hand, the zodiacal light is known to be nearly symmetrical about the ecliptic; thus Blackwell and Ingham [1961] find that the plane of symmetry is inclined at 1°.5 to the ecliptic with its node at about 120° longitude, which very nearly coincides with the invariable plane of the solar system.