NEW ORLEANS — Saturn’s iconic rings are a recent addition. Final data from the Cassini spacecraft, which flew between the planet and the rings this year before plunging into the gas giant’s atmosphere, show the rings are around a few hundred million years old and less massive than previously thought.
Those findings suggest the rings are probably the remnants of at least one moon, rather than ancient remains of the stuff that formed the planet. The results were presented at the fall meeting of the American Geophysical Union on December 12 and 13.
For decades, scientists puzzled over the age and origins of Saturn’s rings (SN: 11/12/16, p. 10). If the rings had formed with Saturn some 4 billion years ago, a constant bombardment of debris from the more distant solar system should make the icy bands appear darker than they do. But scientists thought the rings were too heavy to have formed relatively recently, when there was less material available than in the solar system’s youth for Saturn to pull into the rings.
Cassini’s final orbits may have settled the issue. In the lead-up to the end of its mission in September, Cassini swooped between Saturn and its rings 22 times (SN Online, 9/15/17). Those daredevil moves let astronomers measure the difference in the gravitational tug the probe experienced from Saturn alone and from the rings and the planet together.
Those measurements reveal that the B ring, which makes up 80 percent of the total ring mass, is
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