How the rain of icy particles is affecting the weather of Saturn.

 

Saturn is a magnificent planet, easily recognizable for its opulent ring system, which can be seen through a small telescope. But what astronomers have recently uncovered is that the rings are not as placid as they appear. It has been discovered that the icy ring particles are raining down onto Saturn’s atmosphere, heating up the upper atmosphere in the process. This breakthrough conclusion was reached after researchers studied data from four NASA planetary missions spanning 40 years, which were then combined with observations from the Hubble Space Telescope in ultraviolet light. This discovery may help researchers gain insights into similar ring systems encircling planets orbiting other stars, as their rings would be too far away to be seen, but ultraviolet light spectroscopy of the planets could offer valuable clues.

For over 40 years, the secret of Saturn’s heating atmosphere has been hiding in plain view, but Utilizing observations from NASA’s Hubble Space Telescope, the retired Cassini probe, Voyager 1 and 2 spacecraft, and the retired International Ultraviolet Explorer mission, this scientist was able to deduce that Saturn’s vast ring system is what is causing heat to be generated within its upper atmosphere. This interaction between Saturn and its rings has never been seen before in the solar system and could potentially be used as a tool in predicting if planets around other stars have ring systems similar to Saturn’s.

The telltale evidence of something contaminating and heating Saturn’s upper atmosphere is an excess of ultraviolet radiation, seen as a spectral line of hot hydrogen. Scientists hypothesize that this is due to icy ring particles raining down onto Saturn’s atmosphere as a result of the impact of micrometeorites, solar wind particle bombardment, solar ultraviolet radiation, and electromagnetic forces picking up electrically charged dust. This all happens under the influence of Saturn’s gravitational field pulling these particles into the planet. NASA’s Cassini probe made its final plunge into Saturn’s atmosphere in 2017 and measured the atmospheric constituents, confirming that many particles were indeed falling in from the rings.

The recent study conducted by Lotfi Ben-Jaffel of the Institute of Astrophysics in Paris and the Lunar & Planetary Laboratory, University of Arizona, which was published in the Planetary Science Journal on March 30th, has revealed a surprising connection between Saturn’s rings and its upper atmosphere. Using data from the Cassini Probe, Ben-Jaffel discovered that the slow disintegration of the rings is having a major impact on the atomic hydrogen content of the planet. According to him, this phenomenon is caused by ring particles cascading into the atmosphere, thereby modifying its composition and heating it at certain altitudes through collisional processes with atmospheric gasses.

Ben-Jaffel’s conclusion required a complex gathering of data from various sources to be conclusively proven, he had to draw on archival ultraviolet-light (UV) observations from four different space missions that had studied Saturn. This included measurements from the two NASA Voyager probes in the 1980s, which at the time were dismissed as noise in the detectors. In addition, observations from the Cassini mission, which arrived at Saturn in 2004, provided additional UV data on the atmosphere. Further pieces of the puzzle were provided by Hubble and the International Ultraviolet Explorer (IUE), which launched in 1978 and was a collaboration between NASA, ESA and UK’s Science and Engineering Research Council. Despite these multi-source observations, there remained a question as to whether what was being seen was an illusion or a true phenomenon on Saturn. Ben-Jaffel’s conclusion answered this question once and for all.

Ben-Jaffel’s key to solving the jigsaw puzzle came in the form of measurements from Hubble’s Space Telescope Imaging Spectrograph (STIS). By comparing the STIS UV observations of Saturn to the distribution of light from multiple other space missions and instruments, he was able to successfully calibrate archival UV data from all four space missions that have observed Saturn. After calibrating the various data points, Ben-Jaffel was surprised to discover that the spectra were consistent across all missions, revealing a common reference point for the rate of energy transfer from the atmosphere as measured over decades. This discovery allowed him to accurately plot the different light distribution data together, finally solving the jigsaw puzzle.

For the past four decades, UV data covering multiple solar cycles has been used by astronomers to study the Sun’s seasonal effects on Saturn. By compiling and calibrating all the data, Ben-Jaffel found that the UV radiation levels remain consistent, regardless of the position of the planet. As such, this indicates that the steady “ice rain” from Saturn’s rings is likely to be the best explanation. The results of these findings are expected to be applied to other exoplanets in order to search for evidence of ring systems, which could yield valuable information about the atmospheres of distant worlds. Ultimately, these results could provide new insight into how ring systems affect the atmospheres of planets outside our own Solar System.