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Published June 1987 | public
Journal Article

Aperture synthesis observations of Saturn and its rings at 2.7-mm wavelength


We present 2.7-mm interferometric observations of Saturn made near opposition in June 1984 and June 1985, when the ring opening angle was 19° and 23°, respectively. By combining the data sets we produce brightness maps of Saturn and its rings with a resolution of 6″. The maps show flux from the ring ansae, and are the first direct evidence of ring flux in the 3-mm wavelength region. Modelfits to the visibility data yield a disk brightness temperature of 156 ± 5°K, a combined A, B, and C ring brightness temperature of 19 ± 3°K, and a combined a ring cusp (region of the rings which block the planet's disk) brightness temperature of 85 ± 5°K. These results imply a normal-to-the-ring optical depth for the combined A-B-C ring of 0.31 ± 0.04, which is nearly the same value found for wavelenghts from the UV to 6 cm. About 6°K of the ring flux is attributed to scattered planetary emission, leaving an intrinsic thermal component of ∼13°K. These results, together with the ring particle size distributions found by the Voyager radio occultation experiments, are consistent with the idea that the ring particles are composed chiefly of water ice.

Additional Information

© 1987 Published by Elsevier. Received 15 September 1986, Revised 13 February 1987. We thank the staff of the Owens Valley Radio Observatory for their help with the measurements and for the construction of the superb 3-element millimeter array. We have benefited from many discussions with Don Rudy and Arie Grossman. The reviews from two anonymous referees were very helpful. This work was supported by NSF Grant AST 8601111 and NASA Grants NGL 05-002-003 and NGL 05-002-114.

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