Page 46 - Curriculum Visions Dynamic Book

Farthest from the planet is the E-ring. It extends from 3 to 8 Saturn radii. Inside it is the G-ring, at 2.8 Saturn radii, which shows up only faintly even from close views such as taken by the Voyager spacecraft. Then comes the narrow, shepherded F-ring at 2.33 Saturn radii.
The outermost main ring is the A-ring. It stretches from 2.32 to 2.02 Saturn radii. Within it is the Encke
gap (2.21 Saturn radii) and the Keeler gap (2.26 Saturn radii). The A-ring is separated from the B-ring by a zone with few particles in it called the Cassini division (1.95 to 2.02 Saturn radii). The B-ring is the thickest and broadest of the rings, extending from 1.52 to 1.95 Saturn radii. Within it is the Huygens gap (1.95 Saturn radii). The C- ring (also called the Crepe ring) lies between 1.23 and 1.52 Saturn radii. Within it is the Maxwell gap (1.45 Saturn radii). Inside it the D-ring (1.11 to 1.23 Saturn radii) is visible only in reflected light.
Many of the gaps and even some of the rings have only been known about since spacecraft exploration.
It is believed that the gravitational field of a moon about 10 km across will keep a gap open. One such moon (S18) is found in the Encke gap. Gaps can also be formed by shepherd satellites. For example, the outer edge of the B-ring is shepherded by Mimas. The outer edge of the A-ring is shepherded by Janus.
encke gap A gap between rings around Saturn named for the astronomer Johann Franz Encke (1791–1865).
gravitational field The region surrounding a body in which that body’s gravitational force can be felt.
keeler gap A gap in the rings of Saturn named for the astronomer James Edward Keeler (1857–1900).
shepherd satellites Larger natural satellites that have an influence on small debris in nearby rings because of their gravity.
 This view, which shows Saturn’s C-ring (and
also the B-ring at top
and left) was compiled from Voyager 2. More than 60 bright and dark ringlets can be seen. C-ring material is gray- blue, the colour of dirty ice. Colour differences between this ring and the B-ring indicate differences in composition of the material of the two rings.
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