What Causes Jupiter's Great Red Spot's Bloody Hue? It's a Sunburn

What causes Jupiter's Great Red Spot to actually be red? Scientists have announced that it's likely a product of simple chemicals being broken apart by sunlight in the planet's upper atmosphere. The new findings actually overturn the previous theory for the origin of the spot's color.

Previously, scientists believed that Jupiter's spot received its ruddy hue from reddish chemicals that come from beneath Jupiter's clouds. A new analysis, though, seems to indicate that this isn't the case.

In the lab, researches blasted ammonia and acetylene gases, which are all known to exist on Jupiter, with ultraviolet light. This simulated the sun's effects on these materials at the extreme heights of clouds in the Giant Red Spot, the massive storm that churns on Jupiter.  This produced a reddish material, which the scientists then compared to the Great Red Spot from observations from Cassini's Visible and Infrared Mapping Spectrometer (VIMS). In the end, they found that the light-scattering properties of their results matched a model of the Great Red Spot.

"Our models suggest most of the Great Red Spot is actually pretty bland in color, beneath the upper cloud layer of reddish material," said Kevin Baines, one of the researchers, in a news release. "Under the reddish 'sunburn' the clouds are probably whitish or grayish."

If the spot's red color were due to an upwelling of chemicals formed deep beneath the visible cloud layers, it should have been present at other altitudes. This would make the red spot redder still. Yet it seems as if that isn't actually the case.

In fact, the scientists believe that the red color of the spot may be due to altitude. This red color is only seen in a few other locations on the planet, so it's very possible that it only occurs when clouds of material are high enough in the atmosphere.

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

The findings are being presented this week at the American Astronomical Society's Division for Planetary Science Meeting in Tucson, Arizona.