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A Photometric Model of the Inclined F Ring of Saturn

Author
Scharringhausen, Britt Rebecca
Abstract
Observations by Hubble Space Telescope (HST) of the rings of Saturn during
the 1995 ring-plane crossing revealed a surprising asymmetry in the brightness of
the east and west ansae. As in historical observations, the ring brightness was
nonzero at the time that the rings are observed edge-on. We create a photometric
model of the ring system with the F ring inclined to the main ring plane which re-
produces the observed brightness of the rings and the asymmetry in ring brightness
after the ring-plane crossing.
The F ring is modeled as "ribbon" 60 km tall, of indeterminate radial width,
with a gaussian profile of optical depth as a function of height with an equivalent
depth of D=10+/-4 km and a full width at half maximum of 13+/-7 km. This is the
first estimate of the physical vertical thickness of the F ring, which we find is
approximately 1000 times greater than the main ring thickness.
The model shows that as the Earth crosses the main ring plane, the F ring
dominates the brightness of the system, and that the asymmetry in ring brightness
after the ring-plane crossing is caused by asymmetric absorption of light from the
main rings by the front of the F ring.
The model gives post-crossing asymmetries in good agreement with the HST
data, but fails to reproduce the small asymmetries in ring brightness observed
before the ring-plane crossing. The model profiles of ring brightness plotted vs.
horizontal distance from the center of Saturn show many of the features observed in
the HST profiles. However, the F ring in this model is longitudinally symmetric,
and does not include the many clumps or arcs that have been observed in the
real F ring. It therefore cannot reproduce many of the small-scale variations seen
in the HST profiles. It may be that these small features are responsible for the
asymmetries observed before the ring-plane crossing.
Description
Philip Nicholson
Joseph Burns
Riccardo Giovanelli
Peter Gierasch
Date Issued
2006-10-31Subject
saturnshine; reflectance; Saturn; rings; F ring; photometry; ring-plane crossing
Type
dissertation or thesis