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Saturn is the most distant of the five
planets known to ancient stargazers. In 1610, Italian
Galileo Galilei was the first astronomer to gaze at
Saturn through a telescope. To his surprise, he saw
a pair of objects on either side of the planet, which
he later drew as "cup handles" attached to the planet
on each side. In 1659, Dutch astronomer Christiaan Huygens
announced that this was a ring encircling the planet.
In 1675, Italian-born astronomer Jean Dominique Cassini
discovered a gap between what are now called the A and
B rings.
Like Jupiter,
Uranus, and Neptune, Saturn is a gas giant. It is made mostly of hydrogen
and helium. Its volume is 755 times greater than Earth's.
Winds in the upper atmosphere reach 500 meters per second
in the equatorial region. (In contrast, the strongest
hurricane-force winds on Earth top out at about 110
meters per second.) These super-fast winds, combined
with heat rising from within the planet's interior,
cause the yellow and gold bands visible in its atmosphere.
Saturn's ring system is the most extensive
and complex in our solar system; it extends hundreds
of thousands of kilometers from the planet. In fact,
Saturn and its rings would just fit in the distance
between Earth and the Moon. In the early 1980s, NASA's
two Voyager spacecraft revealed that Saturn's rings
are made mostly of water ice, and they found "braided"
rings, ringlets, and "spokes" - dark features in the
rings that seem to circle the planet at a different
rate from that of the surrounding ring material. Some
of the small moons orbit within the ring system as well.
Material in the rings ranges in size from a few micrometers
to several tens of meters.
Saturn has 31 known natural satellites
(moons). The largest, Titan, is a bit bigger than the
planet Mercury. Titan is shrouded
in a thick nitrogen-rich atmosphere that might be similar
to what Earth's was like long ago. Further study of
this moon promises to reveal much about planetary formation
and, perhaps, about the early days of Earth as well.
In addition to Titan, Saturn has many
smaller "icy" satellites. From Enceladus, which shows
evidence of surface changes, to Iapetus, with one hemisphere
darker than asphalt and the other as bright as snow,
each of Saturn's satellites is unique.
Saturn, the rings, and many of the satellites
lie totally within Saturn's enormous magnetosphere,
the region of space in which the behavior of electrically
charged particles is influenced more by Saturn's magnetic
field than by the solar wind. Recent images by NASA's
Hubble Space Telescope show that Saturn's polar regions
have aurorae similar to Earth's Northern and Southern
Lights. Aurorae occur when charged particles spiral
into a planet's atmosphere along magnetic field lines.
The next chapter in our knowledge of Saturn
is already under way, as the Cassini/ Huygens spacecraft
began its journey to Saturn in October 1997 and will
arrive on July 1, 2004. The Huygens probe will descend
through Titan's atmosphere in late November 2004 to
collect data on the atmosphere and surface of the moon.
Cassini will orbit Saturn more than 70 times during
a four-year study of the planet, its moons, rings, and
magnetosphere. Cassini/Huygens is a joint NASA/European
Space Agency mission.
Related Links:
Source: NASA
Last Updated : 08.20.2003
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Distance from the Sun:
(Semimajor axis of orbit)
1,426,725,400 km
9.53707032 A.U.
Radius:
60,268 km
(9.449 of Earth's radius)
Volume:
755 (Earth = 1)
Mass:
568.51 x 1027 g
Density:
0.70 gm/cm3
Surface Gravity:
896 cm/s2
Escape Velocity:
35.49 km/s (at equator)
Sidereal Rotation Period:
0.44401 day
Sidereal Orbit Period:
29.447498 years
Mean Orbit Velocity:
9.6724 km/s
Orbit Eccentricity:
0.05415060
Orbit Inclination:
2.48446 degrees
Equatorial Inclination:
26.73 degrees
Atmospheric Temperature (at level with
pressure = 1 bar):
134 K
Major Atmospheric Constituents:
H2, He
Natural Satellites:
1. Pan
2. Atlas
3. Prometheus
4. Pandora
5. Epimetheus
6. Janus
7. Mimas
8. Enceladus
9. Tethys
10. Telesto
11. Calypso
12. Dione
13. Helene
14. Rhea
15. Titan
16. Hyperion
17. Iapetus
18. Phoebe
19. Ymir
20. Paaliaq
21. Siarnaq
22. Tarvos
23. Kiviuq
24. Ijiraq
25. Thrym
26. Skadi
27. Mundilfari
28. Erriapo
29. Albiorix
30. Suttung
31. S/2003 S1
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