Simplify the following text for a Grade 12 native English-speaking person.
Original: However , the interiors of Great Dark Spots are relatively cloud-free , and unlike Jupiter 's spot , which has lasted for hundreds of years , their lifetimes appear to be much shorter , forming and dissipating once every few years or so .
Simplified: However , the insides of Great Dark Spots are mostly cloud-free , and unlike Jupiter 's spot , which has lasted for hundreds of years , their lifetimes appear to be much shorter , forming and disappearing once every few years or so .