Six Centuries Old Spiral of Vertical Corrugations in Saturn's C-Ring

Details Six Centuries Old Spiral of Vertical Corrugations in Saturn's C-Ring Six Centuries Old Spiral of Vertical Corrugations in Saturn's C-Ring

Dec 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p12b..01m&link_type=abstract

American Geophysical Union, Fall Meeting 2011, abstract #P12B-01

Physics

[5744] Planetary Sciences: Fluid Planets / Orbital And Rotational Dynamics, [5749] Planetary Sciences: Fluid Planets / Origin And Evolution, [5759] Planetary Sciences: Fluid Planets / Rings And Dust, [6022] Planetary Sciences: Comets And Small Bodies / Impact Phenomena

Scientific paper

Likely evidence of nearly six centuries old collision of captured cometary material with Saturn's Ring C is uncovered in recent Cassini Radio Science ring observations. Three Cassini ring occultation experiments were especially designed so that radio signals transmitted by Cassini to the Earth pass through the rings when the rings are nearly closed as viewed by the ground receiving stations of the NASA Deep Space Network (DSN). In this special geometry, the long path of the radio signals through the rings enhances sensitivity to detection of very tenuous ring material and allows ~400 meters resolution profiling of its radial structure. The observations uncover previously undetectable quasi-periodic optical depth undulations in 4 sub-regions of the innermost ~4000 km of Ring C (~74,480-77,740 km). The structure modulates a tenuous background optical depth of ~0.05 and has peak-to-peak fluctuations < ~0.01, making detection possible only in the case of these 3 special occultations (ring opening angle of 4.8, 4.8, and 1.9 degrees; Cassini Revs 123, 125, and 133, respectively). The structure is detectable at two observation wavelengths (0.94 and 3.6 cm), at multiple observing DSN ground stations, and in data from all 3 occultations. It's characterized by two interfering "tones" of spatial wavelength ~1.3 and ~1.2 km. The wavelength increases slowly with ring radius. The behavior appears consistent with presence of vertical corrugations 4-10 meters in height likely caused by a past ring tilting event (collision with cometary debris) and subsequent differential nodal regression of particle orbits. Time evolution of the perturbations creates a tightly wound spiral pattern of ring height variations which when probed by the radio signals yield the observed tenuous quasi-periodic optical depth fluctuations. The corrugations model was proposed by Hedman et al. [Science 332, 2011] to explain intriguing 30-50 km wavelength structure observed in Cassini images (ISS) across Ring C. The RSS wavelength-radius behavior is in general agreement with the corrugation model prediction; however, important differences persist (ring mass effect?). The much shorter RSS corrugation wavelength compared with ISS implies a separate ring tilting event that is older by ~600 years (late 1300's), and the two tones separation suggests two sub-events ~50 years apart. Together with reported detection of similar corrugations within the tenuous Jovian rings [Showalter et al., Science 332, 2011], the collective observations suggest that these ring-plane-tilting events may not be rare.

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