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This image of Jupiter's white ovals BC and DE was taken by the Galileo spacecraft
Click on image for full size
JPL/NASA

White Oval Trains

The white ovals seem to drift eastward faster than the underlying current which carries other cloud formations in the South Temperate Zone (STZ). Since their birth , the ovals have changed both their appearance ., and the rate of speed at which they drift to the east. The table below shows that the ovals have gradually slowed their rate of drift since their formation.

Oval FA drifted the fastest, and by 1987 was on the other side of Jupiter from where they were born. Oval BC is next eastward-most oval. Oval BC is also the biggest of the classic ovals. Oval BC and oval DE drift at different speeds, thus one might expect that they might run into each other. It seems however that for 60 years, BC and DE have had close encounters, coming to within 18 degrees of each other, but repel each other when they get too close. One will speed up, or the other will slow down so that they always stayed apart.

The three classic ovals are centered at -33 degrees in the southern hemisphere. Other white ovals in the vicinity are situated slightly southward of these three. Since BC is the largest of the ovals it seems to hog the space within the STZ, and not allow the other white ovals, WO1, WO2, and DE to get by. The picture shows a Hubble mosaic in which BC is the eastward-most member, with a train of white ovals trailing along behind.

In 1998, BC and DE had their final close encounter and merged to form a new oval called BE.

Oval FA Drift rate
1958 0.60 deg/day
1960 0.54 deg/day
1979 (Voyager) 0.39 deg/day
1996 (Galileo) 0.13 deg/day

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