Why is Saturn’s atmosphere so warm? Cassini data could explain

Although we are learning more than ever before about the other planets in our solar system, there are still plenty of mysteries to unwind. One open question is why exactly the atmosphere of gas giants like Saturn is so warm, even when the planet is located far from the sun.

Saturn’s atmosphere is composed primarily of hydrogen, with a smaller amount of helium and traces of methane and water ice. It has highly variable temperatures, with some regions being up to 80 degrees Celcius in temperature and others as low as -250 degrees Celsius. Saturn is also home to some of the strongest winds in the solar system, with wind speeds of over 1,100 miles per hour.

The planet’s atmosphere temperatures are an ongoing mystery though, as it is located so far from the sun that it can’t receive much heat from the star. So what is keeping its atmosphere warm?

This false-color composite image shows auroras (depicted in green) above the cloud tops of Saturn's south pole. The 65 observations used here were captured by Cassini's visual and infrared mapping spectrometer on Nov. 1, 2008.
This false-color composite image shows auroras (depicted in green) above the cloud tops of Saturn’s south pole. The 65 observations used here were captured by Cassini’s visual and infrared mapping spectrometer on Nov. 1, 2008. ASA/JPL/ASI/University of Arizona/University of Leicester

A new analysis of data from NASA’s Cassini probe suggests that auroras may be responsible. Like the Northern Lights here on Earth, other planets also have auroras in which solar winds interact with the magnetosphere. In the case of Saturn, as solar winds interact with charged particles from its moons, they create electric currents which not only create the auroras but also generate heat.

The high winds of Saturn play a role as well, by distributing the energy produced by the electrical currents at the poles around the rest of the planet. At the poles, the currents generate enough heat to make the atmosphere twice the temperatures that would be expected if they were heated only by the sun.

“The results are vital to our general understanding of planetary upper atmospheres and are an important part of Cassini’s legacy,” lead author Tommi Koskinen, a member of Cassini’s Ultraviolet Imaging Spectrograph (UVIS) team, said in a statement. “They help address the question of why the uppermost part of the atmosphere is so hot while the rest of the atmosphere – due to the large distance from the sun — is cold.”

The results are published in the journal Nature Astronomy.

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