On the Interpretation of Mercury Observations at Wavelengths of 3.4 and 19 MM

Abstract

view Abstract Citations (2) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS On the Interpretation of Mercury Observations at Wavelengths of 3.4 and 19 MM Morrison, David Abstract Observations made at wavelengths of 3.4 and 19 mm of the microwave phase effect of Mercury are both found to be compatible with a single, basically lunar, set of thermal properties for the planet. Microwave observations of the planet Mercury showing a variation of brightness temperature with phase angle at wavelengths of 3.4 and 19 mm have been recently pub- lished (Epstein, Soter, Oliver, Schorn, and Wilson 1967; Kaftan-Kassim and Kellermann 1967). Gary (1967) has pointed out that the two sets of measurements are incompatible when they are interpreted by means of a simple model for thermal behavior at the planet's surface. I have found that this incompatibility is removed when more realistic thermal models are used in the reduction and interpretation of the data. Treatment of the thermal behavior of Mercury is greatly complicated by the high eccentricity of its orbit and by the spin-orbit coupling, which appears to produce a solar day on Mercury exactly two orbital periods in duration (see, e.g., Dyce, Pettengill, and Shapiro 1967; Soter and Ulrichs 1967). The most striking consequence is that the ob- served brightness temperature will depend not only on phase angle but also on a second celestial-mechanical variable, the heliocentric longitude of Mercury. In a previous paper (Morrison and Sagan 1967; hereinafter referred to as "Paper I"), Carl Sagan and I, using a computer-generated set of thermal models of the planet, discussed the nature of this variation and presented quantitative predictions of disk-integrated brightness temperature as a function of wavelength. Both sets of observed data were originally published to show a dependence of bright- ness temperature, TB, on a single variable, the phase angle `I, and in both a least-squares fit was made to an equation of the form TB= To+z~Tcos(~-~o)°K Publication: The Astrophysical Journal Pub Date: May 1968 DOI: 10.1086/149582 Bibcode: 1968ApJ...152..661M full text sources ADS |