No. 73: Jan-Feb 1991
In late September, 1990, a large white spot appeared on Saturn. Soon, this blemish spread into an oval 21,000 kilometers in length. By early November, it had developed into a planet-encircling band. Apparently, Saturn had "burped," expelling hot gases from its interior. [Saturn emits 50% more heat than it absorbs from the sun.] So far, this is not too beguiling to the anomalist. But now it seems that other white spots, not as large, have been recorded in 1876, 1903, 1933, and 1960. Could the white-spot phenomenon be periodic--like a percolator? More food for thought is found in Saturn's orbital period around the sun: 29.4 years -- not too different from the potential "burp" cycle! (Anonymous; "New White Spot on Saturn Grows, Changes," Science News, 138:325, 1990. Also: Brown, William; "Giant Bubble of Gas Rises through Saturn's Atmosphere," New Scientist, p. 22, October 20, 1990.)
Reference. Historical observations of white spots on Saturn are covered in our handbook: Mysterious Universe. To order, visit: here.