Interplanetary observers have noted that gas giant Jupiter has looked a little naked of late -- it's mysteriously lost one of its iconic stripes.

The anomaly is noticeable for anyone with even a "relatively small telescope," according to The Planetary Society, although what constitutes a "small telescope" for the Planetary Society doesn't necessarily fit under a Christmas tree.

Jupiter's disrobing began somewhere around June last year when the South Equatorial Belt began to fade. By May this year, it had disappeared completely, leaving only the North Equatorial Belt protecting Jupiter's modesty.

It was common knowledge that the belt was disappearing, but flirty Jupiter ducked behind the sun for three months and it was only in recent weeks that eager observers could see to what extent its belt had vanished.

Noted Jupiter watcher Anthony Wesley -- the man who discovered its "scar" last year -- has tracked the disappearing belt from his back yard two hours south of Sydney, Australia. And it's his before-and-after photos which are the most likely you'll come across on the web if you search for the phenomenon.

"It was obvious last year that it was fading. It was closely observed by anyone watching Jupiter," he said. "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.

While exciting for astronomers, it's not uncommon: Jupiter has lost or regained one of its belts every 10 or 15 years.

"The question now is when will the South Equatorial belt erupt back into activity and reappear?" Mr Wesley said, adding that it could be anywhere up to 15 years.

For more, see the full story on News.com.au.