Welcome to the new version of CaltechAUTHORS. Login is currently restricted to library staff. If you notice any issues, please email coda@library.caltech.edu
Published April 16, 1993 | public
Journal Article

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


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.

Additional Information

© 1993 American Association for the Advancement of Science. 15 September 1992; Accepted 19 January 1993. We acknowledge the National Space Science Data Center (NSSDC) and the imaging-team leader from the Voyager project, B. A. Smith, for providing the Voyager images used in this analysis. C.D.B. thanks the National Academy of Sciences-National Research Council associateship program for providing the opportunity to process these data while at the NASA Goddard Space Flight Center.

Additional details

August 20, 2023
October 19, 2023