New research suggests some of Saturn's icy moons, as well as its famous rings, are surprisingly young. In fact, they may have formed after the reign of the dinosaurs, just 100 million years ago.
"Moons are always changing their orbits. That's inevitable," explained Matija Cuk, principal investigator at the SETI Institute. "But that fact allows us to use computer simulations to tease out the history of Saturn's inner moons. Doing so, we find that they were most likely born during the most recent two percent of the planet's history."
Tidal interactions - the push and pull of gravitational forces - between inner moons and fluids deep in Saturn's interior have altered the planet's moons and rings over time, pulling them farther out or titling them at an angle. Therefore, researchers were able to calculate the age of Saturn's rings by studying the orbital tilt of the planet's inner moons.
Previously, it was believed that Saturn's rings were primordial - as old as the planet itself. Researchers were surprised to learn that such a prominent feature of one of the largest planets in our solar system could be a recent development.
To learn more, SETI researchers built a model to simulate the changes in the orbits of Saturn's icy inner moons and rings over time. When they looked at the orbits of some of Saturn's inner moons and rings - including Tethys, Dione and Rhea - they found the orbits are less dramatically altered than previously thought. And relatively small orbital tilts indicate that they haven't crossed many orbital resonances, meaning that they must have formed not far from where they are now.
"So the question arises, what caused the recent birth of the inner moons?" Cuk asks.
Next, researchers estimated the strength of Saturn's tidal forces using geothermal data collected from the Cassini spacecraft, which has observed ice geysers on Saturn's moon Enceladus. This activity, researchers say, suggests Saturn's tidal forces are quite strong.
Based on their findings, researchers estimate that Saturn's inner satellites are not more than 100 million years old, making them younger than Earth's dinosaurs, which first emerged in the Triassic period, 231.4 million years ago.
"Our best guess is that Saturn had a similar collection of moons before, but their orbits were disturbed by a special kind of orbital resonance involving Saturn's motion around the Sun," Cuk explained. "Eventually, the orbits of neighboring moons crossed, and these objects collided. From this rubble, the present set of moons and rings formed."
This research will be published in the Astrophysical Journal.
