2009A&A...495..639G

We present observations of Mercury made with the IRAM 30-m telescope at 3,2 and 1.3mm wavelength (90, 150 and 230GHz) during the years 1985-2005; we derive from these data the disk-averaged brightness temperatures. The observations at 3mm combined with those by Epstein & Andrew (1985, Icarus, 62, 448) allow a separation of the data into 40° wide longitude intervals and by this an investigation of the disk-averaged brightness temperature with Mercury's longitude. From the new mm-wavelength data, and data taken from the literature, we derive the disk-averaged brightness temperature as a function of wavelength. On Mercury's night side a significant decrease in brightness temperature occurs towards shorter wavelengths. We use the three surface models (A,B,C) discussed by Mitchell & de Pater (1994, Icarus, 110, 2) and calculate for the cool and hot surface region the corrresponding diurnal variation of the disk-averaged brightness temperature at 90GHz. For the same models we calculate the variation of the disk-averaged brightness temperature with wavelength between 1.3mm and 37mm, on Mercury's midnight side and noon side. Although the scatter in the observations is large, there seems to be a marginally better agreement with model B and A.