The planet Jupiter has lost one of its belts -- the Southern Equatorial Belt (SEB). It's made of mostly ammonia ice, phosphorus, and sulfur, and apparently disappears now and then:
The belt took leaves of absence in both the early 1990s and in 1973, so its disappearance now, if anything, is a bit overdue (it seems to be on a roughly 15-year cycle).
But due to the orbital dynamics of Earth and Jupiter, this particular disrobing was far more abrupt. Jupiter has been hanging out on the other side of the sun since late 2009, obscured from our view for the last few months. The belt disappeared while Jupiter was hiding, making for quite a drastic change in appearance when it recently re-emerged.
http://www.popsci.com/science/article/2010-05/while-hiding-behind-sun-jupiter-loses-one-its-belts | Image: Anthony Wesley