Saturn is renowned for its rings, easily visible through an ordinary telescope. Now, using observations collected over 40 years, scientists have discovered that the planet’s iconic rings may not be as calm as they look, uncovering a never-before-seen interaction between the planet and its iconic rings.
Scientists collated archival observations of Saturn to discover that the planet’s vast ring system is heating its upper atmosphere, a phenomenon that has not been seen anywhere in the solar system before.
Arriving at this conclusion required piecing together ultraviolet (UV) light observations from four NASA planetary missions. This included data from the Voyager 1 and 2 spacecraft that flew by Saturn in the 1980s, measuring UV excess that, at the time, was considered noise, and the Cassini mission that arrived at Saturn in 2004 and collected UV data over several years. Additional data came from the International Ultraviolet Explorer, launched in 1978, and the Hubble Space Telescope.
From readings provided by the Cassini probe, scientists already knew that particles in Saturn’s rings were slowly falling in towards the planet. What was unexpected was how the rings’ disintegration affected the planet’s levels of atomic hydrogen. Atomic hydrogen appears as single atoms rather than molecules, making it extremely reactive.
“Though the slow disintegration of the rings is well known, its influence on the atomic hydrogen of the planet is a surprise,” said Lofti Ben-Jaffel, lead author of the study. “From the Cassini probe, we already knew about the rings’ influence. However, we knew nothing about the atomic hydrogen content.”
Using high-resolution measurements from the Hubble Space Telescope’s Imaging Spectrograph (STIS) to tie the archival data together was key to the discovery. The precise STIS observations were used to calibrate the archival data obtained by Cassini and the Voyager craft. The resulting image revealed an excess of UV radiation, seen as a spectral line of hot hydrogen in Saturn’s atmosphere that indicates atmospheric heating.
For the scientists, the best explanation for Saturn’s atmospheric heating was a steady rain of icy particles falling onto the planet from its rings, drawn in by its gravitational pull.
“Everything is driven by ring particles cascading into the atmosphere at specific latitudes,” said Ben-Jaffel. “They modify the upper atmosphere, changing the composition.”
It’s hoped that the unexpected interaction between Saturn and its rings can be used to determine if exoplanets orbiting other stars possess Saturn-like ring systems. Although they’d be too far away to see, UV light spectroscopy of a planet could be used to indicate their presence.
“We are just at the beginning of this ring characterization effect on the upper atmosphere of a planet,” said Ben-Jaffel. “We eventually want to have a global approach that would yield a real signature about the atmospheres on distant worlds. One of the goals of this study is to see how we can apply it to planets orbiting other stars.”
The study was published in the Planetary Science Journal.
Source: NASA