Galileo first pointed his tiny telescope at Saturn in July of 1610. Since then, the rings of the giant planet have become one of the great, enduring mysteries of our solar system.The ring system is divided into several visually different radial zones: the outer zone (visible to an Earth observer), is known as the A-ring, while the brighter, inner zone is known as the B-ring. Between these two zones we can sometimes see the gap known as the Cassini division; on an exceptional viewing night, we may see an inner, semitransparent ring, the C or Crepe ring.
Beyond the A, B, C and E-rings, which can be seen or imaged from Earth-bound telescopes, Saturn has several other distinct rings ( the D, F and G-rings ) detected in the images from Pioneer and Voyager.
Why are the rings there at all? How did the rings form and how stable are them? So far, we have only bits and pieces of answers and much speculation about these questions.what are they made of?
Ground-based infrared spectral studies of the A and B rings show that they are composed largely of very nearly pure water ice, making them very similar to several Saturn's inner satellites.Studies of the color distribution (as a sign of compositional variation) in the main rings show that the ring system is not completely uniform in its makeup and that some sorting of materials within A and B rings exists.Why such a nonuniform composition exists is unknown.
Today, we know that much of the ring mass is in particles from a few centimeters to a few meters in diameter; while boulders more than 10 meters in diameter do not comprise much of the mass of Saturn's ring system.the origin of the ringsAmong the early notions about the rings' origin was a theory by Edouard Roche. He suggested that the rings were fragments left over from a moon that had at one time orbited Saturn and then broke up because of the tremendous stresses by Saturn's huge gravitational field.
The Roche theory does not hold up well, however. If the rings were the result of the numerous comets captured and destroyed by Saturn's gravity, why are Saturn's rings so different in nature from the rings of the other giant planets?
Over their lifetime, the rings should present a great amount of carbonaceous and silicate debris brought by comets and asteroids. Yet their composition seems almost entirely to be water ice.
Another issue concerns the stability of the ring system. The effects of torque and gravitational drag, along with the loss of momentum via collisional processes should have produced a system only one-tenth to one-hun-dredth the age of the solar system it-self.
If this hypothesis is correct, then we cannot now be observing a ring system around Saturn that formed when the solar system coalesced. Saturn's rings (as well as the rings of all the other large planets ) may have formed and dissipated many times since the beginning of the solar system: the ring systems could be in a constant, steady state of renewal and regeneration.
Cassini science objectives at Saturn's rings
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text and images : readapted from "the ringed world"
