Space Station Info >> Physical Characteristics Of Saturn's Rings
Physical Characteristics Of Saturn's Rings
The rings can be viewed using
a quite modest modern telescope or with a good
pair of binoculars. They extend from 6,630 km
to 120,700 km above Saturn's equator, and are
composed of silica rock, iron oxide, and ice particles
ranging in size from specks of dust to the size
of a small automobile. There are two main theories
regarding the origin of Saturn's rings. One theory,
originally proposed by Édouard Roche in
the 19th century, is that the rings were once
a moon of Saturn whose orbit decayed until it
came close enough to be ripped apart by tidal
forces (see Roche limit). A variation of this
theory is that the moon disintegrated after being
struck by a large comet or asteroid. The second
theory is that the rings were never part of a
moon, but are instead left over from the original
nebular material that Saturn formed out of. This
theory is not widely accepted today, since Saturn's
rings are thought to be unstable over periods
of millions of years and therefore of relatively
recent origin.
While the largest gaps in the
rings, such as the Cassini division and Encke
division, could be seen from Earth, the Voyagers
discovered the rings to have an intricate
structure of thousands of thin gaps and ringlets.
This structure is thought to arise from the
gravitational pull of Saturn's many moons
in several different ways. Some gaps are cleared
out by the passage of tiny moonlets such as
Pan, many more of which may yet be undiscovered,
and some ringlets seem to be maintained by
the gravitational effects of small shepherd
satellites such as Prometheus and Pandora. |
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Other gaps arise from resonances
between the orbital period of particles in the
gap and that of a more massive moon further out;
Mimas maintains the Cassini division in this manner.
Still more structure in the rings actually consists
of spiral waves raised by the moons' episodic
gravitational perturbations.
Data from the Cassini space probe
indicates that the rings of Saturn possess their
own atmosphere, independent of that of the planet
itself. The atmosphere is collected of molecular
oxygen gas (O2) and is thought to be a product
of the disintegration of water ice from the rings
into its components, oxygen and hydrogen.
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The Dark Side Of The Rings
Compare images from the Cassini spacecraft taken
in March and October 2004, and a Pioneer 11 picture
from 1979:
Cassini spacecraft: March 27,
2004; Frontlit rings. See both the shadow of Saturn
on the rings, and the outline of the rings onto
the planet. The thick B ring is the brightest
part of the ring system.
Pioneer 11 spacecraft: September
1, 1979; Backlit rings, showing the overall darkness
of the rings from this angle. The thickest parts
of the rings are almost imperceptible.
Cassini spacecraft: October 27,
2004; Backlit rings in detail. The thick B ring
appears darkest from this side.
The side of
Saturn's rings that is lit by the Sun looks very
dissimilar to the backlit side, which is darker
generally and appears almost black in the thick
B ring. From Earth, we cannot be glad about this
because the Earth cannot view Saturn from an angle
that displays the backlit side of the rings, and
our only views of it are from spacecraft. In 2004,
the Cassini spacecraft open the first views of
the backlit side in 25 years.
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