Jupiters Great Red Spot, which has tantalized astronomers for centuries, may be caused by something as surprisingly mundane as ultraviolet (UV) tanning at extremely high altitude, say researchers at NASAs Jet Propulsion Laboratory (JPL).

New analysis of NASA Cassini mission observations made during a December 2000 Jupiter flyby, coupled with ground-based lab experiments, point to very high altitude solar photolysis (or the molecular breakup) of ammonia and hydrocarbons at the top of this puzzling red vortex, located in our largest planets southern hemisphere.

High altitude UV radiation from the sun photolyzes ammonia and hydrocarbons, such as methane, in close proximity with each other and in the process creates a bright red cyanide-like molecule, Kevin Baines, a planetary scientist and JPL Cassini team member, told Forbes.

Research suggests effects of sunlight produce the color of Jupiters Great Red Spot. The features clouds are much higher than those elsewhere on the planet, and its vortex nature confines the reddish particles once they form. Image credit: NASA/JPL-Caltech/ Space Science Institute

This week, Baines outlined his and colleagues new hypothesis about the chemical processes that drive the oval-shaped Great Red Spot during a divisional meeting of the American Astronomical Society (AAS) in Tucson. Baines says this whole process depends on having aerosols, particularly ammonia ice particles, lofted upwards to a very high part of the atmosphere where the sunlight is not filtered by overlying gases. As a result, he says, the clouds inside are more susceptible to UV photolysis.

The Red Spot reaches a very high altitude; about 50,000 ft higher than other [nearby] clouds, said Baines. The sunlight is more powerful and direct and

Baines and colleagues used spectral images of the Red Spot, taken by Cassinis Visible and Infrared Mapping Spectrometer (VIMS) to gain new insight into the Red Spots inner workings and as a basis of comparison for their ground-based lab work.

Using a JPL lab, the team performed UV photolysis of acetylene and ammonia, both of which are found in Jupiters atmosphere, and were able to recreate the colors that they see in the planets signature spot.

But why is this Great Spot Red?

This upper layer cooks and turns red, says Baines. As he explains, ammonia-laced clouds whirl around this rarefied upper atmospheric layer in which UV radiation splits an atom of hydrogen from a molecule of ammonia. This free hydrogen atom in turn then runs around and couples with carbon and hydrogen atoms stripped from broken molecules of methane (or some other hydrocarbon) to create a form of red cyanide; providing the Red Spot with its color.

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Jupiter's Great Red Spot Likely One Big UV 'Sunburn'