December 16, 2004
This sequence of nine true-color, narrow-angle images shows the varying appearance of Jupiter as it rotated through more than a complete 360-degree turn. The smallest features seen in this sequence are no bigger than about 380 kilometers (about 236 miles).
Rotating more than twice as fast as Earth, Jupiter completes one rotation in about 10 hours. These images were taken on Oct. 22 and 23, 2000. From image to image (proceeding left to right across each row and then down to the next row), cloud features on Jupiter move from left to right before disappearing over the edge onto the nightside of the planet. The most obvious Jovian feature is the Great Red Spot, which can be seen moving onto the dayside in the third frame (below and to the left of the center of the planet). In the fourth frame, taken about 1 hour and 40 minutes later, the Great Red Spot has been carried by the planet's rotation to the east and does not appear again until the final frame, which was taken one complete rotation after the third frame.
Unlike weather systems on Earth, which change markedly from day to day, large cloud systems in Jupiter's colder, thicker atmosphere are long-lived, so the two frames taken one rotation apart have a very similar appearance. However, when this sequence of images is eventually animated, strong winds blowing eastward at some latitudes and westward at other latitudes will be readily apparent. The results of such differential motions can be seen even in the still frames shown here. For example, the clouds of the Great Red Spot rotate counterclockwise. The strong westward winds northeast of the Great Red Spot are deflected around the spot and form a wake of turbulent clouds downstream (visible in the fourth image), just as a rock in a rapidly flowing river deflects the fluid around it.
The equatorial zone on Jupiter is currently bright white, indicating the presence of clouds much like cirrus clouds on Earth, but made of ammonia instead of water ice. This is very different from Jupiter's appearance 20 years ago, when the equatorial zone was more of a brownish cast similar to the region just to its north.
At the northern edge of the equatorial zone, local regions colored a dark grayish-blue are places where the ammonia clouds have cleared allowing a view to deeper levels in Jupiter's atmosphere. Interrupting these relatively clear regions is a series of bright arrow-shaped equatorial plumes. The most obvious one is visible just above and to the right of center in the third and ninth frames. These plumes resemble the `anvil' clouds that accompany common summer thunderstorms on Earth, although the Jovian plumes are much bigger, and their somewhat regular spacing around the planet suggests an association with a planetary-scale wave motion. The southwest-northeast tilt of these plumes suggests that the winds in this region act to help maintain the eastward winds at this latitude.
In the dark belt north of the equatorial zone, a turbulent region with a white filamentary cloud is visible in the sixth frame, indicating rapidly changing wind direction. Several white ovals are visible at higher southern latitudes (toward the bottom of the fourth, fifth, and sixth frames, for example). These ovals, like the Great Red Spot, rotate counterclockwise and are similar in some respects to high-pressure systems on Earth.
When these images were taken, Cassini was about 3.3 degrees above Jupiter's equatorial plane, and the Sun-Jupiter-spacecraft angle was about 20 degrees.
JPL manages the Cassini mission for NASA's Office of Space Science, Washington, D.C. JPl is a division of the California Institute of Technology in Pasadena.
Credit: NASA/JPL/University of Arizona. (PIA02825A)
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