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 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 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.
The belts are composed of ammonia ice, with a little sulfur and phosphorus thrown in. Scientists aren't quite sure how to account for them - one theory is that they are simply gaps in higher, paler clouds that allow the darker, deeper levels to show through.
It's not the first time the belt has disappeared - indeed, it happens every three to fifteen years. it last went missing in the early 1990s, and before that in 1973.This time, though, the disappearance happened as the planet spent a three-month period behind the sun, so that on its emergence the transformation appears rather more sudden.Over the next few months, we can expect to see a white spot appear which will gradually get stretched out by the planet's 350mph winds to form a new SEB.
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