The left axis represents the planet’s surface. This diagram shows the locations of the ring systems of the four giant planets. We do not know which explanation holds for any given ring, although many scientists have concluded that at least a few of the rings are relatively young and must therefore be the result of breakup.įigure 12.25 Four Ring Systems. Close to the planet (see Figure 12.25), tidal forces can tear bodies apart or inhibit loose particles from coming together. In either theory, the gravity of the planet plays an important role. The second hypothesis, which takes the reverse perspective, suggests that the rings are made of particles that were unable to come together to form a moon in the first place. Tidal forces then pulled the fragments apart, and they dispersed into a disk. A passing comet or asteroid might have collided with the moon, breaking it into pieces. First is the breakup hypothesis, which suggests that the rings are the remains of a shattered moon. There are two basic ideas of how such rings come to be. Because of these interactions, we see phenomena such as waves that move across the rings-just the way water waves move over the surface of the ocean. However, in the main rings of Saturn and Uranus the particles are close enough to exert mutual gravitational influence, and occasionally even to rub together or bounce off each other in low-speed collisions. If the ring particles were widely spaced, they would move independently, like separate moonlets. In fact, it is better not to think of a ring rotating at all, but rather to consider the revolution (or motion in orbit) of its individual moonlets. Thus, the inner particles revolve faster than those farther out, and the ring as a whole does not rotate as a solid body. What Causes Rings?Ī ring is a collection of vast numbers of particles, each like a tiny moon obeying Kepler’s laws as it follows its own orbit around the planet. In this section, we focus on the two most massive ring systems, those of Saturn and Uranus. Jupiter’s ring and at least one of Saturn’s are merely transient dust bands, constantly renewed by dust grains eroded from small moons. The Uranus and Neptune ring systems, on the other hand, are nearly the reverse of Saturn’s: they consist of dark particles confined to a few narrow rings with broad empty gaps in between. Saturn’s large ring system is made up of icy particles spread out into several vast, flat rings containing a great deal of fine structure.
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