Jupiter has lost one of its prominent stripes, leaving its southern half looking unusually blank. Scientists are not sure what triggered the disappearance of the band.
Jupiter's appearance is usually dominated by two dark bands in its atmosphere – one in the northern hemisphere and one in the southern hemisphere.
But recent images of Jupiter taken by amateur astronomers show that the southern band – called the south equatorial belt – has disappeared.
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.
This is not the first time the south equatorial belt has disappeared. It was absent in 1973 when NASA's Pioneer 10 spacecraft took the first closeup images of the planet and also temporarily vanished in the early 1990s.
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.
This article originally appeared on New Scientist.
Image: Anthony Wesley