Saturn's "String of Pearls” After Five Years: Still There, Moving Backwards Faster in the Voyager System

Details Saturn's "String of Pearls” After Five Years: Still There, Moving Backwards Faster in the Voyager System Saturn's "String of Pearls” After Five Years: Still There, Moving Backwards Faster in the Voyager System

Oct 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010dps....42.4103b&link_type=abstract

American Astronomical Society, DPS meeting #42, #41.03; Bulletin of the American Astronomical Society, Vol. 42, p.1039

Astronomy and Astrophysics

Astronomy

Scientific paper

Since July 2005, the Visual Infrared Mapping Spectrometer (VIMS) onboard the Cassini Orbiter has been following an enigmatic feature centered at 33.9 degrees (planetocentric ) north latitude. Observed in detail on 14 occasions between July 2005 and July 2010, the feature is seen only in the 5-micron thermal window which probes large-particle clouds down to the ˜ 4-bar level. This feature is comprised of a main cloud layer near 1.5-3 bar which has 21-25 regularly spaced, near- uniformly-sized, circularly-shaped clearings which together span, on average, 94 degrees of longitude. In VIMS 5-micron imagery, which observes the warm glow of Saturn generated at depth, these regularly spaced and shaped clearings appear bright while the surrounding cloud, observed in silhouette, appears dark- hence the colloquial name "String of Pearls". Each clearing is about 1 degree of longitude (˜900 km) wide, and is, on average over the five-years period, 4.3 degrees of longitude from its neighbor. In latitude, adjacent pearls are typically 0.4 degrees - or about 1 pearl radius - apart. At various times over the past five years of observations, the longitudinal length has varied from 76 to 104 degrees and the mean separation between clearings has varied from 3.6 to 5.0 degrees, while the mean latitude of the structure has ranged from 32.9 to 34.8 degrees - or by 2 mean diameters of the pearls. The pearl structure moves retrograde in the Voyager system (Desch and Kaiser, Geophys. Res. Lett 8, 253-256, 1981) with an average speed over five years of 21.84 ± 0.02 m/s. Since late 2007, the mean latitude increased from 34.0 ± 0.2 to 34.5 ± 0.2 deg as the retrograde speed increased from 21.73 ± 0.09 m/s to 22.02 ± 0.08 m/s, making it the fastest moving retrograde feature observed by Cassini/VIMS in non-polar regions.

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