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Science 16 April 1993:
Vol. 260. no. 5106, pp. 326 - 329
DOI: 10.1126/science.260.5106.326
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Articles

The Drift of Saturn's North Polar Spot Observed by the Hubble Space Telescope

John Caldwell 1, Benoit Turgeon 1, Xin-Min Hua 2, Christopher D. Barnet 2, and James A. Westphal 3

1 Space Astrophysics Laboratory, Institute for Space and Terrestrial Science, and Department of Physics and Astronomy, York University, North York, Ontario, Canada M3J 1P3
2 Space Astrophysics Laboratory, Institute for Space and Terrestrial Science, North York, Ontario, Canada M3J 3K1
3 Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125

Polar projections of 50 images of Saturn at 889 nanometers and 25 images at 718 nanometers taken by the Hubble Space Telescope in November 1990, as well as 3 images at each wavelength taken in June 1991, have been examined. Among them, 31 show the north polar spot, which is associated with Saturn's polar hexagon, in locations suitable for measurement. In each image, planetocentric coordinates of the polar spot were determined, and the movement of the spot with respect to Saturn's system III rotation rate was studied. During the period of observation, the polar spot had first a short-term westward movement and then a long-term eastward drift. The rate of the long-term drift was –0.060 ± 0.008 degrees per day with respect to system III, approximately 50 percent greater than previously determined from Voyager. The original 1980 and 1981 Voyager data were combined with the new Hubble images to form an 11-year base line. The eastward drift over the longer period was –0.0569 degrees per day. The long-term drift could be due to uncertainty in the standard value of the internal rotation period, which is 810.7939 ± 0.148 degrees per 24-hour day. The short-term movement in November 1990 has a rate that is greater in magnitude but opposite in sign and probably represents a real, transient motion of the spot relative to the internal rotation system.

Submitted on September 15, 1992
Accepted on January 19, 1993


THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
Temperature and Composition of Saturn's Polar Hot Spots and Hexagon.
L. N. Fletcher, P. G. J. Irwin, G. S. Orton, N. A. Teanby, R. K. Achterberg, G. L. Bjoraker, P. L. Read, A. A. Simon-Miller, C. Howett, R. de Kok, et al. (2008)
Science 319, 79-81
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