Precise measurements of Cassini's final trajectory have now allowed scientists to make the first accurate estimate of the amount of material in the planet's rings, weighing them based on the strength of their gravitational pull.
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.
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