Saturn's rings are one of the most iconic structures in the solar system, but researchers have never known how or when they formed. A new simulation study shows that Saturn's rings formed much younger than previously thought and that Saturn's moons have undergone rapid changes in the recent universe.
A recently published study suggests that Saturn's rings were formed when two icy moons collided hundreds of millions of years ago. Other evidence suggests that Saturn's orbital dust and some of its moons did not emerge at the same time as Saturn and the rest of the solar system.
High-resolution smoothed particle hydrodynamics simulations (animation below) support the possibility that two icy moons similar to Dio and Rhea collided less than a billion years ago. Most of the resulting debris settled within Saturn's Rocher limit -- the point beyond which gravity would grind any moon-like mass into a ring.
In addition, debris drifting beyond the Roche limit may have coalesced into Saturn's current system of moons. Observations of Saturn and its moons by the Cassini mission, which ended in 2017, have strengthened this theory, with evidence that the rings and moons are very young.
Saturn's rings are constantly receiving foreign material bombarded by micrometeoroids. However, in terms of accumulated amounts, this activity is younger than when Saturn and most of the other planets in the solar system formed 4.5 billion years ago.
Additionally, the rings are losing mass and will eventually disappear as particles drift into the atmospheres of gas giants. The current rate of loss suggests it cannot exist for more than a few hundred million years. In addition, the moon's tidal properties and Rhea's orbital inclination suggest that they took their current form only recently.
The new findings conflict with previous theories about Saturn's rings and moons, which suggested they were as old as the rest of the solar system. Older models suggested that early moons or comets may have collided or broken apart during the chaotic early days of the solar system 3.8 to 4.1 billion years ago, when violent impacts were more common. Another recent formation hypothesis suggests that a Europa-sized moon orbiting between Titan and Europa fell into Saturn's Loche limit about 100 million years ago, but this will require more measurements.
Another interesting discovery about Saturn's moons is that they are heating the planet's atmosphere, according to analysis of data from multiple recent missions. This evidence could help astronomers find ringed planets outside our solar system.
Further analysis of the Cassini data showed that Saturn's moon Enceladus contains all six ingredients needed for life. The research marks the first time scientists have detected phosphorus outside Earth.