Far-infrared spectrophotometry of Saturn and its rings |
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| Authors: | MR Haas EF Erickson DD McKibbin D Goorvitch LJ Caroff |
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| Institution: | MS 245-6, Space Science Division, NASA-Ames Research Center, Moffett Field, California 94035, USA |
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| Abstract: | The spectrum of Saturn was measured from 80 to 350 cm?1 (29 to 125 μm) with ≈6-cm?1 resolution using a Michelson interferometer aboard NASA's Kuiper Airborne Observatory. These observations are of the full disk, with little contribution from the rings. For frequencies below 300 cm?1, Saturn's brightness temperature rises slowly, reaching ≈111°K at 100 cm?1. The effective temperature is 96.8 ± 2.5°K, implying that Saturn emits 3.0 ± 0.5 times as much energy as it receives from the Sun. The rotation-inversion manifolds of NH3 that are prominent in the far-infrared spectrum of Jupiter are not observed on Saturn. Our models predict the strengths to be only ≈2 to 5°K in brightness temperature because most of the NH3 is frozen out; this is comparable to the noise in our data. By combining our data with those of an earlier investigation when the Saturnicentric latitude of the Sun was B′ = 21.2°, we obtain the spectrum of the rings. The high-frequency end of the ring spectrum (ν > 230 cm?1) has nearly constant brightness temperature of 85°K. At lower frequencies, the brightness temperature decreases roughly as predicted by a simple absorption model with an optical depth proportional to ν1.5. This behavior could be due to mu-structure on the surface of the ring particles with a scale size of 10 to 100 μm and/or to impurities in their composition. |
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