| Saturn as seen by the approaching
The sixth planet from the Sun. Saturn is a gas
giant, second only in size to Jupiter
with a diameter more than 9 times that of Earth. It has a spectacular system
of rings and a large collection of moons.
Saturn also has the most flattened shape of any of the major planets. Its
average density is so low that if placed in a big enough tub of water, it
would easily float.
History of observations
Saturn is the most distant of the five planets known to ancient stargazers.
At its brightest (magnitude -1.9), it outshines every star in the sky, including
brilliant Sirius. In 1610, Galileo Galilei
became 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,
Christiaan Huygens announced that this
was a ring encircling the planet. In 1675, Giovanni Cassini
discovered a gap between what are now called the A and B rings.
Saturn's atmosphere consists of 96.3% hydrogen
and 3.25% helium, with traces of methane,
ammonia, ethane, ethylene, and phosphine. Because Saturn is colder than
Jupiter, the more colorful chemicals sink lower in its atmosphere and can't
seen. The result is markings that are much less dramatic than those on Jupiter,
although bands and some small spots are still visible.
Alternate jet streams of east-west and west-east circulation, with speeds
of up to about 1,800 km/h (1,100 mph), have been traced in the motion of
the cloud tops and are responsible for the banded appearance of the planet.
Electrical processes and heat from within Saturn enrich the layered chemical
mixture of the atmosphere which probably transitions from superheated water
near the core to ammonia ice at the observed cloud tops.
At Saturn's center is believed to lie a core of rocky material about the
size of the Earth, but more dense. Around this is a metallic hydrogen shell
some 30,000 km deep, surmounted, in turn, by a region composed of liquid
hydrogen and helium with a gaseous atmosphere some 1,000 km deep.
Saturn has a modest magnetic field similar in strength to Earth's. In 1997
the Hubble Space Telescope observed auroral displays caused by the interaction
between the solar wind and the planetary magnetic field.
|mean distance from Sun
||1,427 million km (886.9 million mi., 9.54 AU)
||1,349 million km (838.6 million mi.)
||1,512 million km (940 million mi.)
||120,536 km (74,913 mi.) / 108,728 km (67,574 mi.)
|equatorial diameter (Earth = 1)
|mass (Earth = 1)
|gravity at cloud tops (Earth =
||35.47 km/s (127,690 km/h, 79,360 mph)
||96.3% hydrogen, 3.25% helium,
traces methane, ammonia, etc
|mean temperature (cloud tops)
||-180 °C (-292 °F)
|number of moons
| With the Sun behind Saturn, the Cassini
probe was able to see two new rings and confirm the presence of two