Saturn’s rings are heating up the planet. Forty years’ worth of observations have shown that particles from the rings are hailing down into the atmosphere, slamming into the hydrogen there and heating it up – but there’s also too much hydrogen, and we don’t know why.
Lotfi Ben-Jaffel at the Paris Institute of Astrophysics and his colleagues made this discovery using archival data from the two Voyager probes, which flew past Saturn in 1980 and 1981, the International Ultraviolet Explorer, which was a space telescope that operated from 1978 to 1996, and the Cassini spacecraft, which orbited Saturn from 2004 to 2017. All of those observations were taken with different types of instruments, though, so they couldn’t be directly compared.
To fix that, Ben-Jaffel and his team took new observations of Saturn using the Hubble Space Telescope. They then calibrated all of the archival measurements so that the UV brightnesses matched what Hubble measured, allowing the light spectrum from each spacecraft to be compared with the others.
“When everything was calibrated, we saw clearly that the spectra are consistent across all the missions,” said Ben-Jaffel in a statement. “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.”
All of the measurements showed extra UV light coming from low latitudes on Saturn, beneath the rings. We know that the rings are slowly disintegrating as they are bombarded by radiation and particles from the sun, micrometeorites and electromagnetic fields, but it seems that the planet itself is being affected by that disintegration as well. As tiny shards of ice rain down from the rings onto the planet, they heat up the upper atmosphere and cause the extra UV brightness.
But the researchers found a mystery as well: those same low latitudes seem to have more hot hydrogen than we know how to explain. It is possible some of this hydrogen comes from the rings or from Saturn’s icy moon Enceladus, in addition to chemistry and mixing deeper down within the atmosphere, but despite all the observations over the years, we just don’t know enough about Saturn’s interior to be sure.