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The B-ring's surface mass density from hidden density waves: Less than meets the eye?
Saturn's B ring is the most opaque ring in our solar system, but many of its
fundamental parameters, including its total mass, are not well constrained.
Spiral density waves generated by mean-motion resonances with Saturn's moons
provide some of the best constraints on the rings' mass density, but detecting
and quantifying such waves in the B ring has been challenging because of this
ring's high opacity and abundant fine-scale structure. Using a wavelet-based
analyses of 17 occultations of the star gamma Crucis observed by the Visual and
Infrared Mapping Spectrometer (VIMS) onboard the Cassini spacecraft, we are
able to examine five density waves in the B ring. Two of these waves are
generated by the Janus 2:1 and Mimas 5:2 Inner Lindblad Resonances at 96,427 km
and 101,311 km from Saturn's center, respectively. Both of these waves can be
detected in individual occultation profiles, but the multi-profile wavelet
analysis reveals unexpected variations in the pattern speed of the Janus 2:1
wave that might arise from the periodic changes in Janus' orbit. The other
three wave signatures are associated with the Janus 3:2, Enceladus 3:1 and
Pandora 3:2 Inner Lindblad Resonances at 115,959 km, 115,207 km and 108,546 km.
These waves are not visible in individual profiles, but structures with the
correct pattern speeds can be detected in appropriately phase-corrected average
wavelets. Estimates of the ring's surface mass density derived from these five
waves fall between 40 and 140 g/cm^2, even though the ring's optical depth in
these regions ranges from 1.5 to almost 5. This suggests that the total mass of
the B ring is most likely between one-third and two-thirds the mass of Saturn's
moon Mimas.Comment: 40 Pages, 21 Figures, Accepted for publication in Icarus, a few typos
fixe
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