The best thermal images of Jupiter's Great Red Spot yet captured have revealed surprising weather and temperature variation within the solar system's most famous storm.

The darkest red part of the spot turns out to be a warm patch inside the otherwise cold storm. The temperature variation is slight: "Warm" in this case translates to -250 degrees Fahrenheit while cold is an even frostier -256 degrees F. But even that difference is enough to create intriguing internal dynamics.

"This is our first detailed look inside the biggest storm of the solar system,” said Jet Propulsion Laboratory astronomer Glenn Orton, who led the new study to be published in Icarus. “We once thought the Great Red Spot was a plain old oval without much structure, but these new results show that it is, in fact, extremely complicated.”

The Red Spot has persisted since at least the late 17th century, when astronomers first saw it. If you'd seen it back then, though, you might have been "tempted to call it the great red sausage," Orton said. "It's shrinking slowly." Still, it's the solar system's longest-lived and largest storm system, wider than three Earths.

Over the past few decades, astronomers had begun to get a handle on the weather patterns around the Great Red Spot, but not inside of it. Previous measurements have indicated that the spot towered over the surrounding cloud cover, much like supercells on Earth.

Scientists have also noticed that its color changes considerably, but what drives the changes — or the famous ruddy complexion in general — is unclear. A leading theory was that sulfurous molecules from deep in the Jovian atmosphere were being lofted by the storm, exposing them to ultraviolet radiation that would break them apart. The newly freed sulfur atoms would then change color and lend the area its distinctive tinge.

But that might not be the case. This latest work shows a clear correlation between the environmental conditions and color, but doesn't help the scientists figure out what chemistry is actually at work, Orton said.

“This is the first time we can say that there’s an intimate link between environmental conditions — temperature, winds, pressure and composition — and the actual color of the Great Red Spot,” Orton's collaborator, Leigh Fletcher, an Oxford astronomer added. “Although we can speculate, we still don’t know for sure which chemicals or processes are causing that deep red color, but we do know now that it is related to changes in the environmental conditions right in the heart of the storm.”

The new thermal images were captured by the VISIR instrument on the European Southern Observatory’s Very Large Telescope in Chile.

Images: 1. ESO/NASA/JPL/ESA/L. Fletcher 2. JPL

Citation: "Thermal Structure and Composition of Jupiter’s Great Red Spot from High-Resolution Thermal Imaging" in * Icarus (forthcoming)*.

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