Using data from several space missions and the Hubble telescope, an astronomer discovered that Saturn's rings are heating its own atmosphere-something that has never been seen before in our solar system.

"The secret has been hiding in plain view for 40 years," a NASA spokesperson announced on Thursday. "But it took the insight of a veteran astronomer to pull it all together within a year."

"Saturn's vast ring system is heating the giant planet's upper atmosphere. The phenomenon has never before been seen in the solar system. It's an unexpected interaction between Saturn and its rings that potentially could provide a tool for predicting if planets around other stars have glorious Saturn-like ring systems, too."

The study used images of Saturn from NASA's Hubble Space Telescope and retired Cassini probe, in addition to the Voyager 1 and 2 spacecraft and the retired International Ultraviolet Explorer mission.

The telltale evidence was an excess of ultraviolet radiation, seen as a spectral line of hot hydrogen in Saturn's atmosphere.

"The bump in radiation means that something is contaminating and heating the upper atmosphere from the outside," explained NASA.

"The most feasible explanation is that icy ring particles raining down onto Saturn's atmosphere cause this heating. This could be due to the impact of micrometeorites, solar wind particle bombardment, solar ultraviolet radiation, or electromagnetic forces picking up electrically charged dust.

"All this happens under the influence of Saturn's gravitational field pulling particles into the planet."

When NASA's Cassini probe plunged into Saturn's atmosphere at the end of its mission in 2017, it measured the atmospheric constituents and confirmed that many particles are falling in from the rings.

"Though the slow disintegration of the rings is well known, its influence on the atomic hydrogen of the planet is a surprise," said the author of a paper published this week in the Planetary Science Journal, Lotfi Ben-Jaffel of the Institute of Astrophysics in Paris and the University of Arizona. "From the Cassini probe, we already knew about the rings' influence. However, we knew nothing about the atomic hydrogen content."

"Everything is driven by ring particles cascading into the atmosphere at specific latitudes. They modify the upper atmosphere, changing the composition. And then you also have collisional processes with atmospheric gasses that are probably heating the atmosphere at a specific altitude."

Ben-Jaffel's conclusion required pulling together archival ultraviolet-light (UV) observations from four space missions that studied Saturn-including Voyager probes that flew by Saturn in the 1980s and measured the UV excess. At the time, astronomers dismissed the measurements as noise in the detectors.

The Cassini mission, which arrived at Saturn in 2004, also collected UV data on the atmosphere over several years. Additional data came from Hubble and the International Ultraviolet Explorer, which was launched by ESA, NASA, and the UK in 1978.

But the lingering question was whether all the data could be illusory, or instead reflected a true phenomenon on Saturn.

"The key to assembling the jigsaw puzzle came in Ben-Jaffel's decision to use measurements from Hubble's Space Telescope Imaging Spectrograph (STIS)," said NASA in a press release. "Its precision observations of Saturn were used to calibrate the archival UV data from all four other space missions that have observed Saturn. He compared the STIS UV observations of Saturn to the distribution of light from multiple space missions and instruments."

Lotfi Ben-Jaffel explained, "When everything was calibrated, we saw clearly that the spectra are consistent across all the missions. This was possible because we have the same reference point, from Hubble, on the rate of transfer of energy from the atmosphere as measured over decades.

"It was really a surprise for me. I just plotted the different light distribution data together, and then I realized, wow - it's the same."

"At any time, at any position on the planet, we can follow the UV level of radiation. This points to the steady "ice rain" from Saturn's rings as the best explanation."

Ben-Jaffel concluded, "We eventually want to have a global approach that would yield a real signature about the atmospheres on distant worlds. One of the goals of this study is to see how we can apply it to planets orbiting other stars. Call it the search for ‘exo-rings.'"

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