Saturn’s rings are one of the most recognizable features in astronomy. Although much is known about them, they still make headlines from time to time. These include a recent study involving an international team of researchers that could help paint a clearer picture of the interaction between the gas giant and the massive ring system that surrounds it.
For the study, researchers used a combination of data collected between 1980 and 2017 from both active and decommissioned space missions to examine ultraviolet (UV) observations of atomic hydrogen emissions in Saturn’s upper atmosphere, identified as a spectral line from hot hydrogen appear.
What they discovered was a unique view of Saturn and evidence that its massive ring system is responsible for warming the gas giant’s atmosphere. In this case, ice particles rain down from the rings from a combination of Saturn’s immense gravity and other possibilities, including solar ultraviolet radiation, micrometeorite impacts, electromagnetic forces, and bombardment from the solar wind. In fact, NASA’s Cassini confirmed the particle rain from the rings during its atmospheric plunge into Saturn, also known as the “grand finale,” in 2017.
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“Although the slow decay of the rings is well known, its impact on the planet’s atomic hydrogen is surprising. We already knew about the influence of the rings from the Cassini probe. However, we knew nothing about the atomic hydrogen content,” said Dr. Lotfi Ben-Jaffel of the Institute of Astrophysics in Paris and the Lunar & Planetary Laboratory at the University of Arizona and lead author of the study. “Everything is powered by ring particles falling into the atmosphere at certain latitudes. They modify the upper atmosphere and change the composition. And then there are also collision processes with atmospheric gases, which probably heat up the atmosphere at a certain altitude. Ben-Jaffel mentions is likely from a 2018 study that confirmed Saturn could lose all of its rings within the next 100 million years, building on earlier observations from NASA’s Voyager 1 and 2.
The space missions that contributed the UV data used for this study were from NASA’s Hubble Space Telescope, NASA’s retired Cassini spacecraft, the European Space Agency’s retired International Ultraviolet Explorer mission, and NASA’s Voyager 1 and 2 spacecraft. as they flew through the Saturn system in 1980 and 1981, respectively. This means the researchers used data between 1980 and 2017, with scientists initially overlooking data showing atmospheric UV excess measured by Voyager 1 and 2 and him interpreted as noise, and similar data was collected from all missions over the next 37 years.
The long-standing conundrum was trying to determine if all of this data from five space missions over the course of nearly 40 years was accurate or misleading, but Dr. Ben-Jaffel took on the task and decided to use Hubble’s Space Telescope Imaging Spectrograph (STIS). Collecting UV data from Saturn in 2017 and calibrating it with all data going back to 1980.
Composite image of three frames of Saturn taken by Voyager 2 on July 12, 1981 through ultraviolet, violet and green filters. (Source: NASA/JPL) Saturn’s southern hemisphere and underside of the rings, imaged by NASA’s Hubble in 2003. (Source: NASA and E. Karkoschka (University of Arizona))
“Once everything was calibrated, we clearly saw that the spectra are consistent across all missions. This was possible because we at Hubble have the same reference point for decades of measured energy transfer rate from the atmosphere,” said Dr. Ben-Jaffel. “It was really a surprise for me. I just plotted the various light distribution data together and then realized, wow – it’s the same.”
In the end found Dr. Ben-Jaffel the same amount of UV radiation in all data between all space missions. This finding was supported by also examining our Sun’s seasonal effects on Saturn from the various solar cycles over almost 40 years of data.
“We can track UV radiation at any time and anywhere on earth,” said Dr. Ben-Jaffel. “This points to the steady ‘freezing rain’ from Saturn’s rings as the best explanation. We are only at the beginning of this annular characterizing effect on a planet’s upper atmosphere. Ultimately, we want to have a global approach that provides a real signature about the atmospheres of 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’.”
What new discoveries will scientists make about Saturn’s rings in the years and decades to come, and could these be used to hunt for “exo-rings”? Only time will tell, and that’s why we know science!
As always, keep doing science and keep looking up!