• Dwek, Eli
• Fixsen, D. J.

Abstract

We combine observations from the DIRBE and FIRAS instruments on the COBE satellite to derive an annually averaged spectrum of the zodiacal cloud in the 10-1000 μm wavelength region. The spectrum exhibits a break at ~150 μm that indicates a sharp break in the dust size distribution at a radius of about 30 μm. The spectrum can be fitted with a single blackbody with a λ<SUP>-2</SUP> emissivity law beyond 150 μm and a temperature of 240 K. We also used a more realistic characterization of the cloud to fit the spectrum, including a distribution of dust temperatures representing different dust compositions and distances from the Sun, as well as a realistic representation of the spatial distribution of the dust. We show that amorphous carbon and silicate dust with respective temperatures of 280 and 274 K at 1 AU, and size distributions with a break at grain radii of 14 and 32 μm, can provide a good fit to the average zodiacal dust spectrum. The total mass of the zodiacal cloud is 2-11 Eg (Eg=10<SUP>18</SUP> g), depending on the grain composition. The lifetime of the cloud, against particle loss by Poynting-Robertson drag and the effects of solar wind, is about 10<SUP>5</SUP> yr. The required replenishment rate is ~10<SUP>14</SUP> g yr<SUP>-1</SUP>. If this is provided by the asteroid belt alone, the asteroids lifetime would be ~3×10<SUP>10</SUP> yr. But comets and Kuiper belt objects may also contribute to the zodiacal cloud.

Topics

• impedance spectroscopy
• amorphous
• Carbon
• grain