It is a simple fact that the rings of Saturn are one of the most intriguing features of our solar system. In fact, planetary rings around other planets are not unknown, but the rings around Saturn are the most extensive planetary ring system we have. They can’t be seen from Earth with the naked eye and were first discovered in 1610 by Galileo Galilei after he perfected the telescope.
Even with his telescope, he was unable to identify the rings clearly and wrote that “[…] the planet Saturn is not alone, but is composed of three [planets].” He also said Saturn had “ears.” To record the fact of his discovery of Saturn’s rings (and to claim credit for it), he used a Latin anagram for, “I have observed the most distant planet to have triple form.”
In 1655 Christiaan Huygens (using a telescope far superior to Galileo’s) was the first to describe the structures around Saturn as a ring. He wrote that “It (Saturn) is surrounded by a thin, flat, ring, nowhere touching, inclined to the ecliptic.” Robert Hooke was another early astronomer who observed the fact that Saturn has rings.
Enough about the discovery, what are the rings? They are made up of billions of small particles ranging in size from a tiny micrometer to ten meters. The particles are composed of 99% water ice with the rest being dust and other chemicals. Saturn’s “ring” is actually many rings which are usually designated by the letters of the alphabet (Ring A, B, C, etc.), at least for the larger more prominent ones.
Those more prominent rings orbit from 7,000 kilometers to 80,000 kilometers above Saturn’s equator. The total mass of all the rings is estimated to be 3 x 10 to the 19th power, but some authorities dispute this saying the accurate mass could be three times as much. In addition to the half dozen or so prominent or “main” rings, there are thousands of “ringlets” in what is really a very complicated structure. Some authorities consider only Rings A, B, and C to be main rings, but then, some of the rings are difficult to classify.
Though a certain amount of accurate observation can be made from Earth, until the Voyager and Cassini space probes were able to make close approaches to the rings, much of the detail we have now was unknown. Rather early on (1675), Giovanni D. Cassini discovered that Saturn’s “ring” was really composed of several rings divided by gaps. The largest of these (between Rings A and B) was eventually named the Cassini Division. It is 4,800 kilometers or 2,980 miles wide.
It is unclear exactly how or when Saturn’s rings were formed. They may be very old, originating at the same time as Saturn itself, left over from the nebular material that formed the planet. One objection to that theory is the fact that they are so bright. Over the eons since Saturn’s formation, the inflow of meteoric dust would have darkened the rings considerably.
However, some research indicates that Ring B anyway is massive enough to dilute such inflow. Others theorize that ring material gets recycled. Particles clump together, then collide and smash each other apart again, leading to the young appearance. The formation could be as recent as 100 million years.
Another interesting theory is that Saturn’s rings were once a moon with an unstable orbit. It eventually approached close enough that the planet’s massive gravity pulled it apart through tidal forces. A variant of that idea is that the moon was smashed by a collision with a large asteroid or comet, the comet contributing its ice to the mix. As recently as December 2010, it was suggested by National Geographic that Saturn’s rings might be the remains of a large moon that was stripped of its icy shell before crashing into the mother planet.
In spite of the detailed information the three space probes sent home, questions still remain. Saturn’s rings remain an intriguing phenomenon, a fact that makes them all the more interesting. And one of the beautiful photographs sent back by the probes would make an excellent addition to the décor of any astronomy buff.
