How Did Saturn Get Its Rings?

Scientists have identified seven major rings, named for the first seven letters of the alphabet, which are made up of many more, thinner “ringlets.” Although they appear solid from a distance, each ring is actually composed of individual bits of ice along with dust and fragments of space rock. These particles range in size from a tiny speck to perhaps as much as one halfmile (0.8 km) wide. The space objects that form the rings whiz around the planet at high speeds—up to thousands of miles per hour.

How Saturn got its rings is still open to debate. The NASA spacecraft Cassini, which reached Saturn in 2004, could provide answers. Cassini’s research suggests that the outer E Ring is formed, in large part, from pieces of ice that break off from Enceladus, one of Saturn’s known 53 moons. Closer to the planet’s surface, some rings seem to be formed by particles that break off other moons when small meteoroids collide with them.

Several theories that explain how some rings formed rest on the Roche limit, which is based on a calculation first made by the 19th-century French astronomer Edouard Roche. In simple terms, the Roche limit means gravity will cause a satellite orbiting a planet to break apart if it approaches within a certain distance of the planet. The rings may be pieces of the material used to form Saturn’s moon. It’s possible some of the matter may have traveled within the Roche limit, the small pieces coming together in ring form. Alternatively, a small moon might have drifted within the Roche limit and Saturn’s gravitational force pulled it apart, creating space debris that formed a ring.

The Cassini mission will last until at least September 2017. Scientists hope the spacecraft will provide more answers about Saturn and its rings.

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