Year: 1965
Type: article
Abstract: Following the inferior conjunction of Venus in June 1964, the microwave emission spectrum of the planet was measured at seven wavelengths in the range ~16 mm, the measurements made with the 10 ft reflector of the Space Sciences Laboratory in Berkeley. The following brightness temperatures were obtained:5600 *51 0K at 16.53 cm, 5950t500K at 14.56 mm, 5300t450K at 13.50 mm, 4510t530K at 12.45 mm, 4950*500 at 11.58 mm, 4120t550K at 9.71 mm, 3900t450K at 8.35 mm. No significant absorption features are evident. In particular, the high disk temperature at 1.35 cm places an upper limit on the amount of water vapor in the lower atmosphere of the planet. Various types of atmospheric constituents are suggested to explain the spectrum. In September 1964, a series of observations of Jupiter, Saturn, and Mercury were made at 1.53 cm with the 85 ft reflector of the Radio Astronomy Laboratory at Berkeley. Saturn, which was close to opposition at the time, was found to have a disk temperature close to that of Jupiter: Ts/Tj=0.94t0.15. The implication is that the emission from Saturn at this wavelength probably arises from layers of saturated ammonia below the visible cloud surface of the planet. Several days observations of Mercury were averaged to obtain an adequate signal to noise ratio. A disk temperature about three times that of Jupiter was obtained: TM/TJ=3.OtO.75. If one takes the temperature of Jupiter as 155 0K at this wavelength, one obtains a temperature of 4650 t 1150 K for Mercury. During the period of observations, the average illumination of the disk was 25 %. Assuming a subsolar temperature of 6200K and a pole darkening proportional to cos+ 0, one finds that the contribution from the illuminated part of the disk amounted to about 1000K. If one assumes that the surface properties of Mercury are similar to those of the moon, one can explain the large dark side contribution to the disk temperature by postulating internal radioactive heat sources which produce a flux of heat at the surface of Mercury some 3040 times that which is observed in the case of the earth. This work has been sponsored by the Office of Naval Research under contracts NONR 222(66) and NONR 222(54).
Source: The Astronomical Journal
DOI: 10.1086/109702
Authors: W. J. Welch, D. D. Thornton
Language: English
Topic: Astro and Planetary Science
Subfield: Space and Planetary Science
Field: Earth and Planetary Sciences
Domain: Physical Sciences
Open Access status: bronze
OpenAlex ID: W2083643448