Babies at 100 million years old: new theories about Saturn’s moons

Until now, astronomers have believed that Saturn’s 62 known moons are as old as the planet: about 4 billion years. New research suggests that some of these moons, along with the rings, are mere babies that may have formed only about 100 million years ago.

Matija Cuk, the principal investigator of the new study from the SETI Institute, says that computer simulations are being used to track the history of the changing orbits of Saturn’s moons, which has led them to believe that these bodies were most likely born only during the most recent 2 percent of the history of the planet. That makes them younger than the dinosaurs.

The moons of Saturn share their orbits with each other, and are affected by the gravity of each other as well as the gravity of the planet. Some taking longer to go around the planet than others. All of those orbits grow over time due to tidal effects, but some of the most important moons, Tethys, Rhea and Dione, have orbits that are smaller than they should be if they had been around for 4 billion years. Their distance from the planet indicates to scientists that those satellites must have formed not very far from where they are now.

Previous simulations by French astronomers in 2012 suggested that some of the inner moons, as well as the rings, might have recent origins. They also found that the moves should have moved to larger orbits by now if they were as old as originally thought.

The latest research team used results from NASA’s Cassini mission in their studies. The spacecraft observed the ice geysers that exist on the Saturn moon Enceladus. Based on the assumption that these geysers are powered by energy that comes directly from tidal interactions, and because the geothermal activity of Enceladus is constant, the conclusion can be drawn that Saturn’s tides are strong. By looking at the position of the major moons of Saturn they determined that the tides would move the satellites the small amount indicated by the simulations in only around 100 million years. This means the major moons of Saturn, except for the distant Titan and Iapetus, were born around the era of the dinosaurs, the relatively recent Cretaceous period.

Cuk says this leads to the next question, which is what caused the birth of those inner moons. He says the team’s best guess is that Saturn had a similar collection of moons before that, but some sort of orbital resonance involving the planet’s orbit around the Sun caused the orbits of some of the moons to cross, resulting in collisions. The present set of moons and rings most likely formed from that rubble.

Image credit: NASA