Saturn’s icy rings likely heat its atmosphere, giving it an ultraviolet glow


The rings that make Saturn such a spectacle probably heat its atmosphere and cause it to glow with ultraviolet waves.

Researchers have discovered an excess of ultraviolet radiation in the northern hemisphere of Saturn, which originates from hydrogen atoms. The emission, known as Lyman-alpha radiation, probably results from water ice, which contains hydrogen, enters the atmosphere from the rings of the planet researchers believe on March 30 in Planetary Science Journal .

The detection of such radiation from a distant world may one day lead to the discovery of a Saturn-like planet orbiting another star.

The key to the discovery came after two spacecraft — the Hubble Space Telescope and Cassini — observed Saturn at the same time in 2017, just before Cassini plunged into the planet’s atmosphere, says Lotfi Ben-Jaffel, an astrophysicist. from the Institute of Astrophysics of Paris.

This allowed Ben-Jaffel and his colleagues to calibrate the ultraviolet detectors on those spacecraft, as well as the detectors on Voyager 1 and Voyager 2, which flew by Saturn in 1980 and 1981, and the International Ultraviolet Explorer, a satellite in Earth’s orbit, which was also observed by Saturn. Comparison of these UV observations revealed a band of excess Lyman-alpha emission spanning 5° to 35°N on Saturn.

The researchers’ explanation for the excess ultraviolet glow is plausible, says Paul Estrada, a planetary scientist at NASA Ames Research Center in Moffett Field, California, who was not involved in the new work.

“We know that material is coming out of the rings,” he says, because Cassini detected it during the spacecraft’s spin on Saturn. “The rings consist mainly of water ice. According to him, this could be the source of the atomic hydrogen that emits the Lyman-alpha radiation that the researchers detected.

When particles of icy rings fall into Saturn’s atmosphere, they carry with them kinetic energy. “They have to release that energy to the surrounding gas,” says Ben-Jaffel, and that energy heats the atmosphere. As the ice particles evaporate, they release additional energy, further heating the atmosphere and causing it to glow in UV radiation. Researchers suspect that radiation also appears in the southern hemisphere of the planet.

All the giant planets in our solar system have rings, but only Saturn’s planets are so bright and beautiful. Astronomers do not yet know whether any of the thousands of worlds orbiting other stars have similarly magnificent rings.

The new discovery could help astronomers identify these spectacular ringed worlds, if they exist. According to Ben-Jafel, future planet hunters could look for the telltale ultraviolet glow of Lyman-alpha radiation, and then follow-up observations could confirm the existence of the rings.

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