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T.W. Momary, K.H. Baines, B.J. Buratti (Jet Propulsion Laboratory/Caltech), C. Griffith, R.H. Brown (University of Arizona, Lunar and Planetary Lab), R. Jaumann (Institute for Planetary Exploration, DLR), P. Drossart (Observatoire de Paris, Meudon), Cassini VIMS Team
One atmospheric science objective of VIMS is to measure windspeeds of cloud features in the Saturnian system at known altitudes, as determined from the 352 spectral bands that VIMS provides. The Titan encounter of 2 July 2004 provided the first opportunity to measure cloud-tracked winds on Titan. Spectral imagery revealed that cloud coverage of Titan was sparse, covering less than 1.5% of the observed sunlit surface. Nevertheless several clouds were followed during the encounter. The most prominent cloud, comprising the bulk of the cloud coverage, was located near the South Pole (~87 degrees south, ~0 degrees lon) and was roughly circular with a diameter of 600 ± 110 km. We tracked this feature over 11 images spanning a 13 hour period. In an attempt to quantify movement of the clouds in a Titanian windstream, we navigated the clouds using three distinct methods: 1) by tracking the brightest pixel in each cloud feature and employing SPICE kernel derived geometry, 2) similarly, by tracking the centroid of the main cloud feature, and 3) for the first time for an outer solar system body, by tracking relative to surface features seen in atmospheric spectral windows, most notably at 2.02 microns. The variable brightness of the most prominent cloud feature and its proximity to the South Pole of Titan make it rather difficult to track accurately. However, preliminary results obtained by tracking the centroid of the main cloud feature, as well as by tracking relative to surface features, indicate that there is little movement over a period of 13 hours. Specifically, we measure a mean windspeed of 0.5 ± 3.3 m/s in the prograde direction.
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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.