Saturn’s icy rings could be much older than they appear due to their resistance to pollution from impacts with rocky debris.
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Hyodo et al. suggest that the apparent youth of Saturn’s rings could be due to pollution resistance, rather than indicative of young formation age. Image credit: NASA / ESA / Hubble / A. Simon, NASA’s Goddard Space Flight Center / M.H. Wong, University of California, Berkeley / OPAL Team.
Saturn’s rings were once thought to be ancient, perhaps formed at the same time as the planet itself — approximately 4.5 billion years ago.
Over time, impacts with micrometeoroids are thought to dirty and darken the rock and ice particles that make up the rings.
However, when NASA’s Cassini spacecraft reached Saturn in 2004, it observed that Saturn’s rings appear to be relatively bright and clean.
“Saturn’s rings have been estimated to be as young as about 100 to 400 million years old according to the hypothesis that non-icy micrometeoroid bombardment acts to darken the rings over time and the Cassini observation indicated that the ring particles appear to be relatively clean,” said Dr. Ryuki Hyodo from the Institute of Science Tokyo and colleagues.
“These young age estimates assume that the rings formed out of pure water ice particles with a high accretion efficiency of impacting non-icy micrometeoroid material.”
In the new study, the researchers simulated collisions between micrometeoroids and icy ring particles using computer models.
They found that high-speed impacts can lead to vaporization of the micrometeoroids, with the vapor then expanding, cooling, and condensing within Saturn’s magnetic field to form charged nanoparticles and ions.
The team’s simulations revealed that these charged particles then either collide with Saturn, are dragged into its atmosphere, or escape the gravitational pull of the planet entirely.
As a result, the scientists suggest that very little of this material is deposited onto the rings, keeping them in relatively clean condition.
They suggest that very low levels of pollution may mean that Saturn’s rings are actually billions of years old and are simply maintaining a more youthful appearance.
Although further research is required, this process could potentially also be occurring in the rings of Uranus and Neptune, as well as on icy moons around giant planets.
“High-velocity impacts leading to the creation of charged nanoparticles and ions could potentially occur in places such as the Uranian and Neptunian rings and icy moons around giant planets,” the authors said.
“While this mechanism may not alter the bulk composition of the impacted target, it suggests that surface composition could change.”
“In addition, new material from impactors may not be efficiently incorporated into the rings or surfaces of moons, but instead transported elsewhere.”
“Therefore, the bulk compositional differences observed in various ring systems among the giant planets could be attributed to their formation processes, for example, when building material comes from the outside of the system, rather than to post-formation dynamics.”
The study was published this week in the journal Nature Geoscience.
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R. Hyodo et al. Pollution resistance of Saturn’s ring particles during micrometeoroid impact. Nat. Geosci, published online December 16, 2024; doi: 10.1038/s41561-024-01598-9
