Red spots

Back on topic of historical observations, here's Cassini's permanent spot on Jupiter. Today we see a red spot, the successor to the red oval of 1879. We assume they're the same spot. Now we're told they are not.

Apparently astronomers since 1713 lost track of the thing - despite their instruments, mathematics, and understanding only improving upon Cassini. If it could be picked up only over a century later - 1831, they say - that must be a different "it".

UPDATE 6/25: Zimmerman and ESA talk structure.