Jupiter's famous sunspot is actually a sunburn

Friday, November 14, 2014, 2:55 PM - Jupiter's Great Red Spot was first observed by astronomer Giovanni Cassini in 1665 and it has been captivating sky watchers ever since.

The spot is a giant storm which has lasted for more than 300 years -- and it's large enough to be picked up by earthly telescopes.

It rotates counterclockwise on a six day cycle with a width that's double that of the Earth's.

Now, scientists from NASA say the Great Red Spot could be the product of chemicals being broken apart by the sun in the planet's upper atmosphere. The new analysis contradicts the popular theory that the spot's colour comes from chemicals beneath the planet's clouds.

NASA is presenting its findings this week at the American Astronomical Society's Division for Planetary Science Meeting in Tucson, Arizona.

The conclusions are based on a combination of data collected by NASA's Cassini space craft.

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In the lab, researchers simulated the effects that the sun's UV light may have on chemicals present on Jupiter.

This created a reddish material, not unlike the reddish hue observed on Jupiter.

"Our models suggest most of the Great Red Spot is actually pretty bland in colour, beneath the upper cloud layer of reddish material," NASA researcher Kevin Baines said in a statement.

"Under the reddish 'sunburn' the clouds are probably whitish or grayish." 

Researchers also think the high altitude of the storm may be influencing its colour.

"The Great Red Spot is extremely tall," Baines said. "It reaches much higher altitudes than clouds elsewhere on Jupiter."

Jupiter's wind transports frozen ammonia particles higher into the atmosphere, exposing them to more UV light. 

The "vortex" nature of the spot also plays a role by trapping particles inside.

This may "both enable and enhance" the reddening, NASA says.