Brightness temperatures of Saturn's disk and rings at 400 and 700 micrometers
Observations at wavelengths longer than 300 microns provide temperature measurements at deeper layers in the atmosphere of giant planets because opacities are reduced. Submillimeter observations of Saturn were made in November 1979 when the inclination angle of the rings was 1.2 degrees. A 55 sec focal plane aperture was used along with two filters with spectral passbands of 300 to 800 microns (mean wavelength approximately 400 microns) and 500 to 850 microns (mean wavelength approximately 700). Mean brightness temperatures of 121 + or - 12 K at 400 microns and 139 + or - 15 K at 700 microns are reported. The brightness temperatures fall below predictions of atmospheric models at shorter wavelengths, requiring an opacity source besides the pressure-broadened hydrogen lines. In combination with measurements at larger inclination angles, the results yield a 400 micrometer brightness temperature for the rings of approximately 75 K.