Fall 1998 Radio Observations of Saturn's Rings:
New Evidence of Ring Wakes

Lawrence A. Molnar (Calvin College), David E. Dunn (U.C. Berkeley), and Jon T. Niehof (Calvin College)
to be presented at the 31st Annual Meeting of the Division for Planetary Sciences, October 10-15, 1999


In Fall 1998 we made Very Large Array observations of Saturn's rings (inclination 15 degr.) at seven wavelengths from 0.7 to 20 cm. The total observing time (four full tracks) was greater than that of our two earlier epochs (1995 and 1997) combined, so that these observations have both greater dynamic range as well as more complete wavelength coverage. We will present the first maps of these observations, and compare them with model maps using the radiative transfer code described in Dunn et al. (this conference).

The most striking new result is the variation of the optical depth of the A ring across the disk of the planet. We interpret this as due to ring wakes that appear more transparent the closer the viewing angle is to end on. By contrast we place strict upper limits on such variation in the C ring, and therefore rule out the presence of similar wakes in that ring. (The B ring shows no variation either, but no conclusions may be drawn about wakes there due to the high optical depth.)

These results are consistent with the expectations of dynamical simulations that wakes should form in the A ring, but not in the C ring where the Keplerian shear is greater. They are also independent of the results of Dunn et al. showing a radial gradient in the ring scattering properties consistent with particle clumping in the A ring, another expectation of dynamical simulations.

Finally, comparison of these results to measurements at smaller inclinations will be used to constrain the ratio of wake heights to separations.

See a movie loop of a theoretical particle distribution seen at 15 degrees inclination and all azimuths in turn.

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