The thermal radio emission from Mercury, Venus, Mars, Saturn, and Uranus

Abstract

The CSIRO 210-ft radio telescope has been used to measure the thermal radio emission from Mercury, Venus, Mars, Saturn, and Uranus between wavelenghts of 6 and 48 cm. No appreciable phase variation was found in the 11-cm radiation from Mercury, indicating that there is little temperature difference between the illuminated and dark hemispheres. The effective surface temperature at 11 cm is between 250° and 300°K. The observations of Venus indicate a slight decrease in effective temperature from about 600°K at centimeter wavelengths to about 500°K at decimeter wavelengths. Little or no change with phase angle was found in the apparent temperature at 11 cm. Observations of Mars at 6, 11, and 21 cm indicate effective temperatures near 200°K, in good agreement with the infrared measurements. The apparent temperature of Saturn was found to increase at longer wavelengths, reaching nearly 200°K at 11 cm and 300°K at 21 cm. As no evidence was found for any linear polarization at 11 cm, it is thought that the radio emission from Saturn is primarily of thermal origin and that the observed increase in temperature at the longer wavelengths over the infrared value of 93°K is due to the higher temperature in the lower regions of Saturn's atmosphere where the long-wavelength radiation presumably originates. Uranus was found to have an equivalent temperature of 130° ± 40° K at 11 cm which, like Saturn, is about twice that expected from solar heating.