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This brief movie, made from narrow angle blue filter images taken during 7 separate Jupiter rotations between October 1 and October 5, 2000, shows the counterclockwise atmospheric motions around the Great Red Spot. The smallest features are about 500 km across. (Images from this time period were released by CICLOPS on October 5 and October 9. See below.)
The spacing of the movie frames in real time is not uniform; some consecutive frames are separated by two Jupiter rotations, and some by one. Each frame consists of multiple Cassini images which have been re-projected and mosaicked together using a simple cylindrical map projection. The movie depicts the motions across a latitudinal band extending from 50 degrees north to 50 degrees south and a longitudinal region 100 degrees in extent -- about one quarter of Jupiter's circumference.
(The still frame is one of the 7 map-projected timesteps in the movie.)
Because the Red Spot is in the southern hemisphere, the direction of atmospheric motion around it indicates that it is a high-pressure center. The eastward and westward motion of the zonal jets, which circle the planet on lines of constant latitude, are also easily seen. As far as can be determined from both Earth-based and spacecraft measurements, the positions and speeds of the jets have not changed for 100 years. Since Jupiter is a fluid planet without a solid boundary, the jet speeds are measured relative to the tilted magnetic field, which rotates, wobbling like a top, every 9 hours 55.5 minutes. The movie shows motions in the magnetic reference frame, so winds to the west correspond to features that are rotating a little slower than the magnetic field, and winds to the east correspond to features that are rotating a little faster.
Small bright clouds appear suddenly to the west of the Great Red Spot. Based on data from the Galileo spacecraft, scientists suspect that these small white features are lightning storms, where falling raindrops create electrical charge. The lightning storms eventually merge with the Red Spot and surrounding jets, and may be the main energy source for these large-scale features. Imaging observations of the dark side of the planet, which are planned for the period of time after closest approach, will search for lightning storms like these.
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA's Office of Space Science, Washington, D.C. The imaging team consists of scientists from the US, England, France, and Germany. The imaging operations center and team lead (Dr. C. Porco) are based at the Space Science Institute in Boulder, Colo.