Chapter 8

Question 1

Radiation darkening

Answer 1

The effect of chemical reactions that result when high-energy particles strike the icy surfaces of objects in the outer solar system. The reactions lead to a buildup of a dark layer of material.

Question 2

A ring

Answer 2

One of three Saturnian rings visible from earth. The A ring from the planet and is separated from the B ring by the Cassini Division.

Question 3

B ring

Answer 3

One of three Saturnian rings visible from earth. The B ring is the brightest of the three and lies just past the Cassini Division, closer to the planet than the A ring.

Question 4

C rings

Answer 4

One of three Saturnian rings visible from earth. The C ring lies closest to the planet and is relatively thin compared to the A and B rings

Question 5

Cassini Division

Answer 5

A relatively empty gap in Saturn’s ring system, discovered in 1675 by Giovanni Cassini. It is now known to contain a number of thin ringlets.

Question 6

Encke Gap

Answer 6

A small gap in Saturn’s A ring.

Question 7

Roche limit

Answer 7

Often called the tidal stability limit, the Roche limit gives the distance from a planet at which the tidal force (due to the planet) between adjacent objects exceeds their mutual attraction. Objects within this limit are unlikely to accumulate into larger objects. The rings of Saturn occupy the region within Saturn’s Roche limit.

Question 8

Ringlets

Answer 8

Narrow region in Saturn’s planetary ring system where the density of ring particles is high. Voyager discovered that the rings visible from Earth are actually composed of tens of thousands of ringlets.

Question 9

F ring

Answer 9

Faint narrow outer ring of Saturn, discovered by Pioneer 11 in 1979. The F ring lies just inside the Roche limit of Saturn and was found by Voyager 1 to be made up of several ring strands apparently braided together.

Question 10

Shepherd satellites

Answer 10

Satellite whose gravitational effect on a ring helps preserve the ring’s shape. Examples are two satellites of Saturn, Prometheus and Pandora, whose orbits lie on either side of the F ring.

Question 11

D ring

Answer 11

Collection of very faint, thin rings, extending from the inner edge of the C ring down nearly to the cloud tops of Saturn. This region contains so few particles that it is completely invisible from Earth.

Question 12

E ring

Answer 12

A faint ring, well outside the main ring system of Saturn, which was discovered by Voyager and is believed to be associated with volcanism on the moon Enceladus.

Question 13

Stellar occultation

Answer 13

The dimming of starlight produced when a solar system object such as a planet, moon, or ring passes directly in front of a star.

Question 14

Plutoids

Answer 14

A dwarf planet orbiting beyond Neptune.