The Structure of Saturn's Poles Determined by Cassini VIMS: Constraints on Winds and Horizontal and Vertical Cloud Distributions.

Details The Structure of Saturn's Poles Determined by Cassini VIMS: Constraints on Winds and Horizontal and Vertical Cloud Distributions. The Structure of Saturn's Poles Determined by Cassini VIMS: Constraints on Winds and Horizontal and Vertical Cloud Distributions.

Oct 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007dps....39.0902b&link_type=abstract

American Astronomical Society, DPS meeting #39, #9.02; Bulletin of the American Astronomical Society, Vol. 39, p.423

Astronomy and Astrophysics

Astronomy

1

Scientific paper

We present new imagery and quantitative results for wind and cloud structures in both polar regions of Saturn, obtained by Cassini/VIMS. For the north pole, currently experiencing winter darkness, only 5-μm thermal images of Saturn's depths near the 3-bar level are useful. Saturn's northern Polar Hexagon, discovered in Voyager imagery by Godfrey (Icarus 76, 335-356, 1988), is a prominent feature, extending downward at least several bars of pressure. The re-acquisition of this feature indicates that the hexagon is a multi-decade, long-lived feature which survives the Saturn seasons. Observed three times over a 12-day period in late 2006, both hexagonal features stay fixed in a rotational system defined by the Voyager-era radio rotation rate (Desch and Kaiser, Geophys. Res. Lett, 8, 253-256, 1981) to within an accuracy of 11 seconds per rotational period. This agrees with the stationary nature of the wave in this rotation system found by Godfrey (1988), but is inconsistent with rotation rates found during the current Cassini era. Individual clouds, observed as dark silhouettes, are seen racing around the edges of the
5-μm-bright hexagon at speeds of 100 m/s. At the south pole, a hurricane-like vortex feature is observed with a deep "eye” of cloud-free skies extending about 1 bar deeper than the surrounding ring of clouds. Discrete clouds at 88 degrees S. planetographic latitude whip around the pole at speeds approaching 200 m/s. In contrast, clouds near 77 degrees S. latitude are nearly stationary. Two distinct types of reflective, discrete clouds are observed interspersed throughout the region: bright clouds at continuum wavelengths from 0.6 to 2.7 μm characterized in our preliminary modeling as having imaginary indices of refraction near 0.002 at 0.7 μm, and spectrally dark clouds with twice that value, indicating different chemical compositions for the two types of cloud particles.

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