The symmetry plane of the zodiacal cloud retrieved from IRAS data

Annual oscillations of 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; also, secondarily, due to the eccentricity of the earth's orbit. Comparing brightnesses at the poles and in the ecliptic (near 90deg elongation) allows to retrieve inclination i and ascending node Ω SP/ecliptic through an inversion technique, with very little model-dependence. The results (i=1.5deg, Ω=90deg) conflict with some of those previously obtained from the same observations by more model-dependent approaches, they do, however, agree with former optical determinations from the D2A satellite and from Tenerife ground-based data. (author). 6 figs., 27 refs