It was there a few months ago—but now it’s gone. Astronomers have no idea why:
Jupiter has lost one of its prominent stripes, leaving its southern half looking unusually blank. […]
The band was present at the end of 2009, right before Jupiter moved too close to the sun in the sky to be observed from Earth. When the planet emerged from the sun’s glare again in early April, its south equatorial belt was nowhere to be seen.
Check it out: