Microwave observations of the disk and rings of Saturn at low inclinations

Details Microwave observations of the disk and rings of Saturn at low inclinations Microwave observations of the disk and rings of Saturn at low inclinations

Dec 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999phdt..........d&link_type=abstract

Thesis (PhD). THE UNIVERSITY OF IOWA, Source DAI-B 60/06, p. 2747, Dec 1999, 147 pages.

Physics

3

Saturn Rings, Radiative Transfer, Interferometry, Microwave Imagery, Saturn Atmosphere, Mie Theory, Brightness Temperature, Monte Carlo Method

Scientific paper

We present two epochs of Saturn observations with the Very Large Array spanning 0.7-21 cm. The first epoch occured at Saturn's autumnal equinox, when the ring inclination was only +2.68°, the second fifteen months later, when the ring inclination was still shallow, -5.0°. In our first epoch we find latitudinal structure on the Saturnian disk at all wavelengths except at 2 cm, although our upper limits cannot rule out structure there as well. The details of the structure has changed dramatically from those that de Pater and Dickel (1991, Icarus, 94, 474) reported were present in the 1980's. The most prominent features are a pair of brightness enhancements just inside the edges of the Equatorial Zone. The second epoch, with more signal to noise, verified the results of the first epoch and discerned latitudinal structure even at the shorter wavelengths. The zonal structure may arise from density or temperature variations, and modeling of the multiple wavelength data may resolve this issue. In the first epoch, the ring system shows some enhanced brightness in the forward direction, especially at smaller radial distances and longer wavelengths. The east-west asymmetry reported by de Pater and Dickel is found to be enhanced in our data for wavelengths greater than 0.7 cm at only the first epoch. We note that while there is good evidence that the radio emission at these wavelengths is scattered emission from the planet, no choice of scattering properties can account for this asymmetry if the particles are randomly distributed. We suggest, therefore, that the asymmetry may be an artifact of multiple scattering by anisotropically distributed ring particles. We present a Monte Carlo code which is sufficiently generalized and may be applied to many scenarios beyond the rings of Saturn. We ran the code for isotropic and Mie scattering ring particles orbiting about Saturn using nominal parameters. Neither model fit the all of the data well. However, a hybrid model between the isotropic and Mie scattering does indeed fit the data well.

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