The properties of large particles in the zodiacal cloud and in the interstellar medium, and their relation to recent IRAS observations
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To explain the scattering of sunlight observed from theF-corona and from the zodiac, the scattering particles must have radii of order 15 μm, and must have an imaginary component of the refractive index that requires the presence of from 5 to 10% of free carbon. The particles, therefore, have a composition very like the material of C 1 carbonaceous chondrites and like extraterrestrial particles which have been recovered from the high atmosphere.
Such particles absorb sunlight, the absorbed solar energy being reradiated in the infrared with a close approximation to black-body emission, even as far into the infrared as 100 μm, a deduction in good agreement with recently published observations from the IRAS satellite.
The IRAS observations at high ecliptic latitudes require similar particles to be present in large quantity in the interstellar medium, ∼106 solar masses or more of them. The presence of such a quantity of material with properties very like the material of the C 1 carbonaceous chondrites is a remarkable outcome of the IRAS observations and is likely to have profound implications in many directions.
KeywordsRefractive Index Large Particle Solar Energy Interstellar Medium Close Approximation
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