Why Not Solid?,
Why Not Flat?, From Voyager
Saturn's rings are wide, but very flat and thin. They are around 45,000 miles wide, but only 500 feet thick. As a result, the rings appear to disappear when they are observed from the side.
Jupiter, Neptune and Uranus all have rings around them, the rings around
Saturn are the most distinguishable in the solar system. They are Saturn's
most distinctive features and make it one of the most beautiful objects in
the solar system. Scientists believe that Saturn's rings are more brilliant than the rings of Jupiter, Uranus, and Neptune because they are newer. Scientists believe the rings may have formed when a moon came to close to Saturn and broke up into tiny little pieces as a result of Saturn's gravity.
The rings, first seen in 1610 by Galileo
Galilei, can be seen with nearly any telescope today. When Galileo first
saw it, he did not know what it was. He described them as "ears" and
"handles". (Today, the Latin word for handles, ansae, still refer
to rings.) In 1656, a Dutch astronomer named Christiaan Huygens using a
stronger telescope was able to see that the "ears" were actually disks of
material around the equator of Saturn. (Yes, an fortunate
discovery...imagine saying "And in this picture, you can see the beautiful
ears of Saturn.")
There are seven rings around Saturn, each
represented by a letter (A-G). The rings are around 20,000 kilometers
wide, but less than 2 kilometers thick. They are believed to be millions
of moonlets, made up of ice, orbiting together. These moonlets are usually
a few kilometers across (Just imagine cars floating around Saturn). The
moonlets are far enough apart so that they appear solid, but in fact, are
not solid. Stars can be seen through them.
Rings A, B, C- the main rings around Saturn.
Rings A and B, the bright ones, are separated by the Cassini
[kah-SEE-nee] Division, the largest gap between the rings discovered by
Giovanni Cassini in 1675. Within the A Ring, there is the Encke [EN-kee]
Division, discovered by Johann Encke in 1837.
Ring D- the faintest and closest to Saturn.
Ring F- the thin, braided one just outside of
Rings G and E- the faint outermost rings.
WHY NOT SOLID?:
Solid rings would be impossible. This
was theoretically proved by James Clark Maxwell. If the rings were just
slightly off center with the planet, the planet's gravitational field
would be unequal. The side of the rings closer to the planet would have a
stronger pull. The other side would have a weaker pull from the planet.
Eventually, the side of the rings closer to the planet would come even
closer to the planet as the planet's gravity pulled it in until KASPLAT!!!
The rings would crash into the planet. Individual moonlets are able to
adjust the planet's gravitational pull by changing speeds to keep in
orbit. This actually occurs in Saturn's rings. It has been observed that
the inner parts of the rings move at a faster speed than the outer
portion. A solid ring would not be able to adjust its speed to maintain
its orbit because it must spin at the same rate everywhere.
WHY NOT FLAT:
are flat because of numerous "collisions" that occur. Rings rarely
collide, but when they are close enough to each other, they have an effect
that causes them to become more circular and lie in the same plane. When
"collisions" between two rings occur, the average velocities of the rings
are averaged (similar to how when a still billiard ball is hit by a cue
ball. The cue ball slows down, while the billiard ball gains speed.) and
become uniform. A spinning planet has a tendency to cause inclined or
eccentric orbits to collide with other orbits of the rings. When this
occurs, the orbit of the rings are less inclined and more circular. After
many "collisions", the rings are now on the same plane and circular, thus
making them flat and round.
From Voyager 1 and 2, up
close pictures of Saturn's rings showed that they were made up of ringlets
(the same as moonlets). The darker bands of the rings are darker because
more material is present. Lighter bands have less material. Another
discovery made by the Voyagers is that the
ringlets do not stay in the same position. They "kink" or "braid". A good
example of this is the thin, braided Ring F. Many who have seen the pictures say that Saturn's rings look like the
grooves of a phonograph record. What do you think? (in
this picture or the colorful one at the top)
A wide angle view of Saturn's rings
by the Voyager 2. You can see all A through F rings.