Temperatures of Zodiacal dust

Abstract

Temperatures of interplanetary dust particles have been determined by calculating the termal emission from dust concentrations according to the “Five Populations of Interplanetary Meteroids” model by Divine ( J. geophys. Res., in press, 1993) and matching it with the observed zodiacal thermal emission. Properties of the meteoroid populations are describned by comparing them with the meteoroid mas distribution measured at 1 a.u., and with zodiacal light observations ranging from 0.3 to 4 a.u. Particle temperatures are assumed as a function of heliocentric distance and particle size. An IR emissivity of 1 has been assumed for aprticles bigger than-one tenth of the considered wavelength and zero for smaller particles. The intensity contributions of the five meteoroid populations are evaluated. The resulting total IR intensity is compared with the intensity of the zoidcal emission as determined either by the Infrared Astronomical Satellite IRAS or by the Zodiacal Infrared Project ZIP. At I a.u., temperatures have been obtained which range from 130 to 190 K and from 380 to 390 K for particles of diameters 10 −4 and 10 −6 m, respectively. Compared with Mie calculations the particle temperatures are between those of a dielectric (obsidian) and a strongly absorbing material (graphite).