Composition 
The mean density of Saturn is one-eighth that of the Earth because the planet consists mainly of hydrogen. The enormous weight of Saturn's atmosphere causes the atmospheric pressure to increase rapidly towards the interior, where the hydrogen gas condenses into a liquid. Closer to the centre of the planet, the liquid hydrogen is compressed into metallic hydrogen, which is an electrical conductor. Electrical currents in this met
allic
hydrogen are responsible for the planet's magnetic field. At the centre of
Saturn, heavy elements have probably settled into a small rocky core with a
temperature close to 15,000° C (27,000° F). Both Jupiter and Saturn are still
settling gravitationally, following their original accretion from the gas and
dust nebula from which the solar system was formed more than 4.5 billion years
ago. This contraction generates heat, causing Saturn to radiate into space three
times as much heat as it receives from the Sun.
THE ATMOSPHERE
OF SATURN
Saturn's atmospheric constituents
are, in order by mass, hydrogen (88 per cent) and helium (11 per cent); and the
remainder comprises traces of methane, ammonia, ammonia crystals, and such other
gases as ethane, ethene (ethylene), and phosphine. Voyager images showed whirls
and eddies of clouds occurring deep in a haze that is much thicker than that of
Jupiter because of Saturn's lower temperature. The temperatures of Saturn's
cloud tops are close to -176° C (-285° F), about 27° C (49° F) lower than those
of such locations on Jupiter.
The movements of Saturnian storm clouds show that the period of
rotation of the atmosphere near the equator is about 10 hr 11 min. Radio
emissions that have been
detected coming from the body of the planet indicate that the body of Saturn and
its magnetosphere rotate with a period of 10 hr 39 min 25 sec. The approximately
28.5-min difference between these two times indicates that Saturnian equatorial
winds have velocities close to 1,700 km/h (1,060 mph).
In 1988, from studies of Voyager photos, scientists determined an odd atmospheric feature around Saturn's north pole. What may be a standing-wave pattern, repeated six times around the planet, makes cloud bands some distance from the pole appear to form a huge, permanent hexagon.
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