The Gaseous Planets
 -------------------------

1, Jupiter
-----------
Diameter=142,800 km or 11.3 times that of Earth.
Jupiter, often called the King of the Planets, is the largest planet in our 
solar system and fifth from the sun. Like the rest of the Gaseous planets, 
Jupiter is composed primarily of the gases hydrogen and helium and has no solid 
surface. Jupiter is unique, however, in the fact that it gives off more energy 
than it receives from the Sun. 1,000 km beneath Jupiter's cloud tops, the 
enormous pressure turns the hydrogen gas into liquid hydrogen. Jupiter spins so 
fast (its day is the shortest of all the planets, at ten hours) that its liquid 
mass bulges outward at the equator. The temperature at Jupiter's cloud tops is -
148 C. Jupiter is also known for its storms; the Great Red Spot is the center of 
a storm system that was first seen more than 300 years ago. Viewed from Earth, 
Jupiter is the fourth brightest object in the sky after the Sun, the Moon, and 
Venus. Jupiter's year is 11 years and 314.96 days long and with it on its huge 
orbit it drags at least 16 moons. The largest four are Europa, Io, Callisto, and 
Ganymede, and only Europa is smaller than our Moon. 

2, Saturn
-----------
Diameter=120,700 km or 9.4 times that of Earth.
Saturn is the sixth planet from the Sun, the second of the gaseous planets, and 
also the second largest planet in our solar system. Like Jupiter, it is composed 
mostly of hydrogen and helium and here too, at 1,000 km below its clouds, the 
hydrogen gas turns into liquid. Saturn is more loosely packed than Jupiter and 
its spin, only slightly slower, gives it the greatest equatorial bulge of all 
the planets. Saturn's day is 10 hours and 41 minutes long, and its year 29 years 
and 167.25 days. It is 1,429,370,000 km from the Sun and the temperature at 
Saturn's cloud tops is -178 C. Saturn is probably the most beautiful planet in 
our solar system, best known for its bright and complex system of rings. These 
measure about 274,000 km across but are only about 15 meters thick. The rings 
are not solid, but made up of billions of ice particles ranging in size from 
that of a sugar grain to that of a house. Saturn has at least 17 moons, the 
largest of which are Titan, Rhea, Iapetus, Dione, and Tethys. 

3, Uranus
------------
Diameter=51,700 km or 4 times that of Earth.
Little was known about Uranus until Voyager 2 was sent there in 1986, because of 
its great distance from us. Uranus shows little cloud activity because it 
generates so little internal heat and also because of a layer of methane-ice 
crystals, like an ice fog, that further acts to block what lies beneath. The 
atmosphere on Uranus is 85% hydrogen and 15% helium. The planet rotates once 
every 16.7 hours and completes an orbit around the sun in 84 years and 3.65 
days; the temperature here is -213 C. Uranus is the only planet to have a tipped 
rotation axis, rotating almost on its side. The planet seems to roll around the 
Sun rather than spin, resulting in each pole experiencing 21 years of sunlight 
and 21 years of darkness! This makes Uranus the planet with the longest winter. 
Uranus also has a system of nine skinny rings, which are nearly invisible from 
Earth but were discovered by accident in 1977 when Uranus passed in front of a 
star and blocked out some of its light. Uranus has 15 satellites, the largest 
being Titania, Oberon, Umbriel, Ariel, and Miranda. 

4, Neptune
--------------
Diameter=48,600 km or 3.8 times that of Earth
Neptune is the eighth planet from the Sun and the last of the giant ones. It is 
so remote that no specific atmospheric feature had ever been seen from Earth 
until its encounter with Voyager 2 in 1989, when the Great Dark Spot was 
discovered. This feature is remarkably similar to Jupiter's Great Red Spot; it 
has the same proportions and lies at the same latitude south of the equator. 
Below the visible surface of Neptune is a bottomless atmosphere of hydrogen and 
helium that, thousands of miles down, eventually merges with a hot slush of 
hydrogen, helium, and water ice sloshing around inside the planet. This core 
region rotates once every 16 hours, but the outer atmosphere spins more slowly 
and at different rates at different latitudes. The differences in the rotation 
create friction that produces heat inside the planet. This in turn causes 
weather, such as the Great Dark Spot. The temperature at Neptune's cloud tops is 
about -216 C; its year about 165Earth years. 

 Like the other giants, Neptune also has rings; there are five of them, 3 
thread-thin ones, and 2 so fuzzy that Voyager 2could barely detect them. Neptune 
has 8 satellites; the largest three are Triton, 1989N1, and Neried. 

5, Pluto
----------
Diameter=2,280 km or 18% that of Earth
Pluto is so small and so far away that it was not even discovered until 1930. It 
is the last planet in the solar system that we know of (it would take 10 years 
to travel there by spacecraft), and it is also the smallest, only about two-
thirds the size of our Moon. Pluto also has a very strange orbit. It takes 
almost 249 years for the planet to go around the Sun and at times it crosses the 
orbit of Neptune, making Neptune the farthest planet in the solar system. 
Pluto's orbit is tilted 17 degrees (see diagram below), the largest tilt of all 
the planets, and this keeps Pluto and Neptune from colliding. From 1979 until 
1999 Pluto is the eighth planet from the Sun and Neptune the ninth. Pluto's 
atmosphere is extremely thin but it does contain methane and the warmest 
temperature there is about -223 C. Pluto's day is 6 Earth days, 9 hours, and 17 
minutes, spinning in the opposite direction of Earth. One satellite, Charon, 
orbits Pluto and it is about half the size of the planet. Pluto's orbit, shown 
in green, is tilted 17 degrees, causing it to come inside the path of Neptune 
(blue) at times, making Pluto the eighth planet for several years at a time.

