The dust production rates of all the known periodic comets, calibrated by the measurements from the 1986 apparition of comet Halley, are ušed to compute their dust input into the region inside the earth orbit, and the resulting dust fluxes at R = 1 AU. The spatial distribution of tho fresh ejecta and the teraporal variations of their accumulation are reconstructed. Tho visible release of dust is evidently insufficient to maintain the zodiacal cloud in equilibrium.
It is suggested that the progressive decay of the dark matter, including extinct cometary nuclei, their fragments, and products of asteroidal collisions, represents the dominant source of
replenishmont of the interplanetary dust complex.
The annual oscillations of the brightnesses observed at 12 and 25 μm by IRAS near the ecliptic poles are mainly due to the inclination of the symmetry plane (SP) of the interplanetary dust cloud upon the ecliptic, but also, secondarily, to the eccentricity of the earth's orbit.
Comparing the brightnesses at the poles and in the ecliptic (near 90° elongation) allows a retrieval of the inclination i and ascending node Ω SP/ecliptic through an inversion technique, with very little model-dependence. The results (i = 1.5°, Ω = 90°) conflict with some of those previously obtained from the same observations by more model-dependent approaches, but they agree with former optical determinations from D2A satellite and from Tenerife
ground-based data.