The bands may normally appear dark simply because pale, high-altitude clouds prevalent in other regions of the planet are missing there, revealing darker clouds below, says Glenn Orton of the Jet Propulsion Laboratory in Pasadena, California. "You're looking into different layers of the cloud structures of the planet," he told New Scientist.
According to this theory, the south equatorial belt disappears when whitish clouds form on top of it, blocking our view of the darker clouds. But it is not clear what causes these whitish clouds to form in the south equatorial belt at some times and not others, Orton says.
The disappearance of the belt comes at a time of widespread – but mysterious – change on Jupiter, which has seen changes to the colour of other bands and spots in its atmosphere. "There has been a lot going on," Orton says.
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