The secret was hidden from view for 40 years. But it took the insight of an experienced astronomer to put it all together over the course of a year, using NASA’s Hubble Space Telescope and the decommissioned Cassini probe, as well as the Voyager 1 and 2 spacecraft and observations of Saturn from the outgoing International Ultraviolet. Explorer mission for retirement.

Discovery: Saturn’s large ring system is warming the giant planet’s upper atmosphere. This phenomenon had never been observed before in the solar system. This is an unexpected interaction between Saturn and its rings, and could potentially be a tool to predict whether planets around other stars also have extraordinary Saturn-like ring systems.

One provable evidence is the excess of ultraviolet radiation in Saturn’s atmosphere, which can be seen as a spectral hot hydrogen line. Rising radiation means that something is polluting and heating the upper atmosphere from the outside.

The most likely explanation is that ice ring particles falling into Saturn’s atmosphere caused this warming. This can be caused by micrometeorite impacts, solar wind particle bombardment, solar ultraviolet radiation, or electromagnetic forces that collect 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 the composition of the atmosphere and confirmed that many particles had fallen from the rings.

“Although the slow decay of the rings is well known, the effect on the planet’s atomic hydrogen is surprising. We already knew the effect of the rings from the Cassini probe. However, we didn’t know anything about the atomic hydrogen content,” he said. .

“It all happens thanks to ring particles cascading into the atmosphere at certain latitudes. They change its composition by changing the upper layers of the atmosphere,” Ben-Jaffel said. “You also probably have processes of collisions with atmospheric gases that heat the atmosphere at a certain height.”

Ben-Jaffel’s conclusion required combining archival ultraviolet (UV) light data from four space missions studying Saturn. This includes observations of NASA’s two Voyager probes that passed by Saturn in the 1980s and measured the ultraviolet excess. At the time, astronomers treated the measurements as detector noise. The Cassini mission, which reached Saturn in 2004, also collected UV data about the atmosphere (over several years). Additional data came from Hubble and the International Ultraviolet Explorer, which was launched in 1978 and is the result of an international collaboration between NASA, ESA (European Space Agency) and the UK Science and Technology Research Council.

But the question was whether the data would be completely misleading or instead reflect a real phenomenon on Saturn.

Ben-Jaffel’s decision to use Hubble Space Telescope Imaging Spectrograph (STIS) measurements was the key to the puzzle. Precise observations of Saturn were used to calibrate archival UV data from four other space missions observing Saturn. He compared STIS UV observations of Saturn with light scatter from many space missions and instruments.

“When everything was calibrated, we were able to clearly see that the spectra were consistent across missions. This is possible because we have the same reference point we got from Hubble for the energy transfer rate from the atmosphere measured over decades.” -I. – Yaffel said. “It really came as a surprise to me. I just combined the different light distribution data together and then I realized, well, it’s the same thing.”

Forty years of UV data cover several solar cycles and help astronomers study the Sun’s seasonal influence on Saturn. By combining and calibrating all the various data, Ben-Jaffel found that there was no difference in the level of UV radiation. “We can monitor the level of UV radiation anywhere on the planet, at any time,” he said. This points to a constant “ice shower” from Saturn’s rings as the best explanation.

“We are only at the beginning of the study of the effect of ring properties on the upper layers of the planet’s atmosphere. Finally, we want to have a global approach that will yield real insights into the atmospheres of distant worlds. One of the goals of this research is to see how we can apply this to planets orbiting other stars. We call this “outer rings.” say.

The Hubble Space Telescope is an international collaborative project between NASA and ESA. The telescope is operated by NASA’s Goddard Space Flight Center in Greenbelt, Maryland. The Space Telescope Science Institute (STScI) in Baltimore runs Hubble’s science operations. STScI is administered by the Association of Astronomical Research Universities for NASA in Washington, DC.