QUESTION:

I wonder what Saturn’s rings are made of?

ANSWER:

            If you ever get an opportunity to peer at Saturn through a telescope, even a small one, you are looking at one of nature’s most majestic sights. You will be inspired, as Galileo was in 1610, when he became the first person to observe the beautiful ring structure of Saturn.

            Four robot spacecraft have visited Saturn. The latest, named Cassini, went in orbit around Saturn in July, 2004. Cassini sent back thousands of colored pictures of the rings and moons of Saturn. Cassini carried a detachable vehicle, Huygens, which parachuted onto the surface of Titan, a moon of Saturn. Stunning pictures of this alien world were sent back by the wheelbarrow sized Huygens.

            The rings of Saturn are composed of ice and some rock and dust. They are 240,000 miles wide but only about 300 feet thick. The smallest particles are smaller than a grain of sand and the largest are about the size of a bus.

            There are between 500 and 1,000 rings, with gaps in the rings. Each little particle could be thought of as a moon. Saturn has 31 “regular” moons, but 6 are considered major moons. Titan is the largest moon and is much bigger than our own Moon.

            We know that the Moon pulls on the Earth and the Earth pulls on the Moon. It is that gravitational tug on each other that causes the tides here on Earth. But tides affect solid objects also. When an object, such as a moon, gets too close to the planet, the tidal forces will tear that object apart and shatter it into thousands of pieces.  

            There is a mathematical rule, termed the Roche limit, that determines how close an object can get to a planet and not be torn apart. The Earth’s Roche limit is about 12,000 miles. Not to worry, though, our Moon is 240,000 miles away.

            Saturn in almost 100 times more massive than our Earth. So the Roche limit extends out quite far from Saturn’s surface. Billions of years ago, moons, rocks, comets, and any other debris that got too close to Saturn was pulverized and trapped in orbits forming the rings. Asteroids and other objects are continually bombarding the solar system. All that stuff gets caught in the ring system.

            The other gas giants of Jupiter, Uranus, and Neptune also have rings around them. They are quite faint and not easily seen. They are more like wispy circles. Saturn has the most material inside that Roche limit, and hence has the most elaborate set of rings.

            There are many gaps in the rings. The biggest gap is Cassini’s Division. From Earth, it looks like a thin black gap in the rings. It was first seen in 1675 by Giovanni Cassini from the Paris Observatory.

            Saturn is now a “morning star”, along with Venus. Look in the Eastern sky just before dawn. Each morning it will appear higher in the sky. If you have a small telescope, the ring tilt is about 19 degrees in December, and Saturn will show off

her magnificent rings.