Millimeter-wavelength observations of minor planets

Bolometer observations at 250 GHz of fifteen minor planets have shown that the emissivity of these objects is close to unity. This results in an independent method to determine the absolute calibration scale of radio observations at mm wavelengths: Applying our results to Mars, the prime calibrator at this wavelength, gives a mean absolute disk temperature at mean solar distance of approximately 210 K. Further, the diameters of circularly symmetric asteroids can be determined or the surface area of asteroids can be estimated assuming some geometric constraints on their shape.