Saturn’s rings are small and can disappear quickly

Cassini mission data suggests that Saturn’s rings are young, possibly only a few hundred million years old, and could disappear in a similar timescale. The rings’ mass, purity, and debris accumulation rates indicate their relatively young age and short lifespan. Two studies show that the rings formed relatively recently and are rapidly losing mass, while a third predicts their disappearance within the next few hundred million years.

While no human could ever have seen Saturn without its rings, in the time of the dinosaurs, the planet may not yet have acquired its iconic accessories – and future Earth dwellers may again know a world without them.

Three recent studies by scientists at NASA’s Ames Research Center in California’s Silicon Valley examine data from NASA’s Cassini mission and provide evidence that Saturn’s rings are both young and ephemeral – in astronomical terms, of course.

The new research looks at the mass of the rings, their “purity,” how quickly incoming debris is added, and how that influences the way the rings change over time. Put those elements together, and one can get a better idea of how long they’ve been around and the time they’ve got left.

Although all four giant planets have ring systems, Saturn’s is by far the most massive and impressive. Scientists are trying to understand why by studying how the rings have formed and how they have evolved over time. Three recent studies by NASA researchers and their partners provide evidence that the rings are a relatively recent addition to Saturn and that they may last only another few hundred million years. Credit: NASA/JPL-Caltech/Space Science Institute

The rings are almost entirely pure ice. Less than a few percent of their mass is non-icy “pollution” coming from micrometeoroids, such as asteroid fragments smaller than a grain of sand. These constantly collide with the ring particles and contribute debris to the material circling the planet. The rings’ age has been hard to pin down, because scientists hadn’t yet quantified this bombardment in order to calculate how long it must have been going on.

Now, one of the three new studies^[1] It gives a better idea of ​​the total rate of arrival of non-glacial material, and thus, how far it must have “polluted” the rings since their formation. This research, which was led by the University of Colorado, Boulder, also indicates that micrometeorites don’t come as fast as scientists think, which means Saturn’s gravity could pull matter more effectively into the rings. This evidence goes on to say that the rings cannot be exposed to this cosmic hailstorm for more than a few hundred million years – a small fraction of Saturn and the solar system’s 4.6 billion years.

Supporting this conclusion is the second paper,^[2] Led by Indiana University, which takes a different angle on the constant beating of the rings by small space rocks. The study authors identified two things that have been largely neglected in the research. Specifically, they were looking at the physics that govern the long-term evolution of rings and found that two important components were the bombardment of micrometeorites and the way the debris from those collisions is distributed within the rings. Taking these factors into account shows that the rings could have reached their current mass in a few hundred million years. The results also indicate that because they are so young, they likely formed when unstable gravitational forces within the Saturnian system destroyed some of its icy moons.

“The idea that Saturn’s iconic major rings might be a recent feature of our solar system has been controversial,” said Jeff Causey, a researcher at Ames and co-author on one of the recent papers. “But our new findings complement a trifecta of Cassini measurements that make this discovery difficult to avoid.” Causey also served as an interdisciplinary scientist on the Cassini mission to Saturn’s rings.

Saturn, then, may have been more than 4 billion years before it adopted its present form. But how long can you count on wearing the beautiful rings we know today?

The Cassini mission discovered that the rings are rapidly losing mass, as material falls from the planet’s deeper regions. Third paper^[3] Also, led by Indiana University, determines for the first time how quickly ringed matter drifts in this direction — and meteorites again play a role. Their collisions with existing ring particles and the way the resulting debris is thrown outward combine to form a kind of conveyor belt for motion that carries ring material towards Saturn. By calculating what all those streaming particles mean for their eventual disappearance into the planet, researchers have come up with some hard news for Saturn: It could lose its rings in the next few hundred million years.

“I think these results tell us that the constant bombardment by all this alien debris not only pollutes the planetary rings, but it should also weaken them over time,” said Paul Estrada, a researcher at Ames and co-author of all three studies. “maybe[{” attribute=””>Uranus’ and Neptune’s diminutive and dark rings are the result of that process. Saturn’s rings being comparatively hefty and icy, then, is an indication of their youth.”

Young rings but – alas! – relatively short-lived, as well. Instead of mourning their ultimate demise, though, humans can feel grateful to be a species born at a time when Saturn was dressed to the nines, a planetary fashion icon for us to behold and study.

References:

“Micrometeoroid infall onto Saturn’s rings constrains their age to no more than a few hundred million years” by Sascha Kempf, Nicolas Altobelli, Jürgen Schmidt, Jeffrey N. Cuzzi, Paul R. Estrada and Ralf Srama, 12 May 2023, Science Advances.
DOI: 10.1126/sciadv.adf8537

“Constraints on the initial mass, age and lifetime of Saturn’s rings from viscous evolutions that include pollution and transport due to micrometeoroid bombardment” by Paul R. Estrada and Richard H. Durisen, 9 May 2023, Icarus.
DOI: 10.1016/j.icarus.2022.115296

“Large mass inflow rates in Saturn’s rings due to ballistic transport and mass loading” by Richard H. Durisen and Paul R. Estrada, 9 May 2023, Icarus.
DOI: 10.1016/j.icarus.2022.115221