Precise measurements of Cassini’s final trajectory have now
That estimate — about 40 percent of the mass of Saturn’s moon Mimas, which itself is 2,000 times smaller than Earth’s moon — tells them that the rings are relatively recent, having originated less than 100 million years ago and perhaps as recently as 10 million years ago.
Their young age puts to rest a long-running argument among planetary scientists. Some thought that the rings formed along with the planet 4.5 billion years ago from icy debris remaining in orbit after the formation of the solar system. Others thought the rings were very young and that Saturn had, at some point, captured an object from the Kuiper belt or a comet and gradually reduced it to orbiting rubble.
The new mass estimate is based on a measurement of how much the flight path of Cassini was deflected by the gravity of the rings when the spacecraft flew between the planet and the rings on its final set of orbits in September 2017. Initially, however, the deflection did not match predictions based on models of the planet and rings. Only when the team accounted for powerful flowing winds deep in Saturn’s atmosphere — something impossible to observe from space — did the measurements make sense, allowing them to calculate the mass of the rings.
News Source: https://news.berkeley.edu/2019/01/17/saturn-hasnt-always-had-rings/
