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The secret is hidden in plain sight for forty years. But it took the foresight of an experienced astronomer to sort it all out in a year, using observations of Saturn from NASA’s Hubble Space Telescope and the retired Cassini probe, as well as the Voyager 1 and 2 spacecraft and the retired International Ultraviolet Orbiter. . Discovery: Saturn’s massive ring system is warming the giant planet’s upper atmosphere.
This phenomenon has not been observed in the solar system before. It’s an unexpected interaction between Saturn and its rings that could help predict whether planets around other stars also have Saturn-like ring systems. Evidence for this is an excess of ultraviolet radiation, which is seen as a spectral line of hot hydrogen in Saturn’s atmosphere. Excess radiation means that something is polluting the upper atmosphere and heating it up from the outside.
The most likely explanation is that ice ring particles falling into Saturn’s atmosphere are causing this warming. This may be due to the impact of micrometeorites, bombardment of solar wind particles, solar ultraviolet radiation, or electromagnetic forces that capture electrically charged dust. All this happens under the influence of Saturn’s gravitational field, which attracts particles to the planet. When NASA’s Cassini probe plunged into Saturn’s atmosphere at the end of its mission in 2017, it measured what made up the atmosphere and confirmed that many particles were falling from the rings.
“Although the slow disintegration of the rings is known, its effect on the atomic hydrogen of the planet is a surprise. From the Cassini probe, we already knew the effect of the rings. However, we knew nothing about the atomic hydrogen content.” Lotfi Ben Javel of the Astrophysical Institute in Paris and the University of Arizona’s Lunar and Planetary Laboratory, author of a paper published March 30 in the journal Planetary Sciences.
“Everything is moved by cascading ring particles in the atmosphere at specific latitudes. They change the upper atmosphere and change its composition,” said Ben Javel. “And then you also have collisions with atmospheric gases that potentially heat the atmosphere at a certain altitude.”
Ben Javel’s conclusion required merging ultraviolet observations from four space missions that studied Saturn. These include observations from two NASA Voyager probes that flew by Saturn in the 1980s and measured the excess of ultraviolet radiation. At the time, astronomers dismissed the measurements as noise in the detectors. The Cassini mission, which arrived at Saturn in 2004, collected ultraviolet data on the atmosphere (over several years). Additional data came from the Hubble and the International Ultraviolet Explorer, which was launched in 1978 and was an international collaboration between NASA, the European Space Agency (ESA), and the UK Science and Engineering Research Council.
But the question remains whether all the data could be misleading, or reflect a real phenomenon on Saturn instead.
The key to solving the puzzle lies in Ben Javel’s decision to use measurements from the Hubble Space Telescope Imaging Spectroradiometer (STIS). Careful observations of Saturn have been used to calibrate archival data from all four other space missions that have looked at Saturn. Compare STIS’ ultraviolet Saturn observations of ultraviolet light distribution for multiple space missions and instruments.
“Once everything was calibrated, we clearly saw that the spectra of all the missions were consistent,” Benn said. “This was possible because we had the same reference point, from Hubble, on the rate of energy transfer from the atmosphere as measured over the decades.” – Javi. “It really came as a surprise to me. I put the different light distribution data together, and then I realized, wow — it’s the same thing.”
Four decades of UV data covering multiple solar cycles helps astronomers study the sun’s seasonal effects on Saturn. By pooling and calibrating all the different data, Ben Javel discovered that there was no difference in the level of UV radiation. “At any time and anywhere on the planet we can monitor the level of ultraviolet radiation,” he said. This points to the constant “freezing rain” from Saturn’s rings as the best explanation.
“We are at the beginning of the impact of this circular characterization on a planet’s upper atmosphere. Ultimately, we want a global approach that results in a true circular characterization signature on distant worlds. One of the goals of this research is to see how we might be able to apply it to planets orbiting other stars. Call it a search for “exo rings.”
The Hubble Space Telescope is an international collaboration project between NASA and the European Space Agency. NASA’s Goddard Space Flight Center in Greenbelt, Maryland, operates the telescope. The Space Telescope Science Institute (STScI) in Baltimore conducts the science activities for the Hubble Telescope. STScI is administered for NASA by the Association of Universities for Research in Astronomy in Washington, DC
source: NASA
