Philips Atlas of the Universe

THE SOLAR SYSTEM

Outside the main system comes Ring F, which is faint

and complex. It is stabilized by two more small satellites,

Prometheus and Pandora, which act as ‘shepherds’ and

keep the ring particles in place. Prometheus, slightly

closer to Saturn than the ring, moves faster than the ring

particles, and will speed up a particle if it moves inwards,

so returning it to the main ring zone; Pandora, on the far

side, will be moving more slowly, and will drag any

errant particle back.

The outer rings (G and E) are very tenuous indeed.

The brightest part of Ring E is just inside the orbit of the

icy satellite Enceladus, and it has even been suggested

that material ejected from Enceladus may have been

concerned in the formation of the ring. It is difficult to

say where Ring E ends; traces of it may extend out to as

far as the orbit of the larger satellite Rhea, more than

500,000 kilometres (312,000 miles) from Saturn.

There has been considerable discussion about the origin

of the rings. According to one theory, they represent the

debris of an icy satellite which wandered too close to

Saturn and paid the supreme penalty, though on the whole

it seems more likely that the rings are formed from

material which never condensed into a larger body. At

any rate, they are there for our inspection, and for sheer

beauty Saturn is unrivalled in the Solar System.

Voyager 2’s image of

Saturn’s F-ring and its small

inner shepherding satellite

Prometheus from a range

of 365,000 km (227,000

miles) taken on 25 August

Rings of Saturn, as seen

from the Cassini spacecraft

on 21 June 2004, nine days

before it entered orbit about

the planet. This natural-

colour image was obtained

from a distance of 6.4 million

kilometres (4 million miles).

The B ring is the bright,

sandy coloured area

stretching from lower left to

upper right.

1981. Prometheus is more
      reflective than Saturn’s
      clouds, suggesting that it is
      an icy, bright-surfaced object
      like the larger satellites and
      the ring particles themselves.

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