Jupiter has lost one of its iconic red stripes and scientists are baffled as to why.
The largest planet in our solar system is usually dominated by two dark bands in its atmosphere, with one in the northern hemisphere and one in the southern hemisphere.
However, the most recent images taken by amateur astronomers have revealed the lower stripe known as the Southern Equatorial Belt has disappeared leaving the southern half of the planet looking unusually bare.
The band was present in at the end of last year before Jupiter ducked behind the Sun on its orbit. However, when it emerged three months later the belt had disappeared.
Jupiter was pictured this month (left) looking unusually bare, compared to July 2009 (right). It has lost its dark red Southern Equatorial Belt although scientists are unclear as to why. The pictures have different tones because they were snapped a year apart.
He said: 'Jupiter with only one belt is almost like seeing Saturn when its rings are edge-on and invisible for a time - it just doesn't look right.'
It is not the first time this unusual phenomenon has been noticed. Jupiter loses or regains one of its belts every ten of 15 years, although exactly why this happens is a mystery.
Jupiter has a complex belt system
These clouds are created by chemicals that have formed at different heights. The highest white clouds in the zones are made of crystals of frozen ammonia. Darker, lower clouds are created from chemicals including sulphur and phosphorus. The clouds are blown into bands by 350mph winds caused by Jupiter's rapid rotation.
Noted Jupiter watcher Anthony Wesley, who spotted an impact spot on its surface last year, has tracked the disappearing belt from his back garden in Australia.
'It was obvious last year that it was fading. It was closely observed by anyone watching Jupiter,' he told The Planetary Society.
'There was a big rush on to find out what had changed once it came back into view.'
Mr Wesley said while it was a mystery as to what had caused the belt to fade, the most likely explanation was that it was linked to storm activity that preceded the change.
'The question now is when will the South Equatorial belt erupt back into activity and reappear?' Mr Wesley said.
The pattern for this happening is when a brilliant white spot forms in the southern zone. Gradually it will start to spout dark blobs of material which will be stretched by Jupiter's fierce winds into a new belt, and the planet will return to its familiar 'tyre track' appearance.
Jupiter will be closest to Earth on September 24, offering stargazers their best chance of seeing it without its stripe
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