Mercury: Thermal emission at radio wavelengths: I. 3.3- and 28-mm observed brightness temperatures and periodicities therein

Measurements of the thermal radio emission from Mercury at 3.3 mm were made on 103 days and at 28 mm on 113 days over a several-year interval. The data can be represented by T B(3.3 mm) = 359 ±4 + 147 ±6 cos (φ + 17 ±2 )° K, SD = 42° K, T B(28 mm) = 374 ±4 + 42 ±5 cos (φ + 36 ±7 )° K, SD = 34° K where the statistical standard errors and deviations are indicated, T B is the brightness temperature, and phi; is the planetocentric phase angle. The estimated absolute calibration uncertainties are 7% (3.3 mm) and 5% (28 mm). Fitting with higher order harmonics of phi; or including the hermocentric longitude of the sub-Earth point does not improve the goodness of fit. Of the fits considered, the two data sets are best represented by multiterm harmonics as a function of time which include terms corresponding to several physically significant periods in the Earth-Mercury relationship. Summaries of measurements at 2.1, 3.1, 13.5, and 37.5 mm by other observers are included.