Saturn Put A Ring On It Relatively Recently, Study Says

Saturn is famous for its lovely rings, but a new study suggests the planet has spent most of its 4.5 billion years without them. From a report: That's because the rings are likely only 10 million to 100 million years old, according to a newly published report in the journal Science that's based on findings from NASA's Cassini probe. Cassini spent some 13 years orbiting Saturn before plunging down and slamming into its atmosphere. During its final orbits, the spacecraft dove between the planet and its rings. That let scientists measure the gravitational effect of the rings and get a good estimate of the ring material's mass.

What they found is that it's only about 40 percent of the mass of Saturn's moon Mimas, which is way smaller than Earth's moon. This small mass suggests that the rings are relatively young. That's because the rings seem to be made of extremely pure water ice, suggesting that the bright white rings have not existed long enough to be contaminated by the bombardment of messy, dirty comets that would be expected to occur over billions of years. Some scientists thought it was possible that darker debris from comets might lie beneath the bright ice, undetectable to their instruments, but this new study shows that isn't the case.

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