What? No pictures!
Some good ones at Space.com along with some reasonable explanations like black spots on Jupiter might not be that uncommon. Especial sense we don't know much about Jupiter's atmosphere.
Hard to imagine those tiny pellets expolding and causing a cloud the size of earth
to appear while being wipped around at 400 mph and not dissipating.
Be sure to check out Eric's photos, they're good. If memory serves me right he lives in Japan and uses a 10" SCT with a UTcam(sp?) from the roof of his residence.
SteveS