The Outer Planets

Jupiter:	Jupiter has the shortest day of all the planets known. It rotates on its axis in 9 hours and 50 minutes (Earth time). This is quite remarkable considering that, as the largest planet, Jupiter’s mass is 318 times the Earth’s mass. A year on Jupiter, however, is around 12 Earth years. None of the outer planets (except Pluto) has a solid surface. Jupiter may have a solid core, but the surface is composed of 90% hydrogen and 10% helium, methane, ammonia, phosphene, water and some other compounds.
	Jupiter has bands of color, which are caused by convection currents. Light bands are hot, rising currents. Darker bands are cooler currents. The great red spot seems to be caused by a hurricane-like storm of reddish gases. Jupiter has crushing air pressure, frequent magnetic storms, and cosmic radiation showers. The temperature on the surface is -250°F, but is -45,000°F near the core. Jupiter has at least 16 moons. Four of these are large and terrestrial, and were observed by Galileo. Of these four, Io has at least 8 active volcanoes and lakes of molten sulfur. Europa appears to be white with a smooth icy surface. Ganymede has a grooved terrain that looks like it was combed. Callisto is covered with ice-filled craters.
Saturn:	Saturn, like Jupiter, has a gaseous surface composed of hydrogen, helium, methane, and ammonia. The rings around Saturn are 102,000 miles wide and 155,000 miles around. They are composed of rocks, boulders and dust covered with frozen gases. Saturn has at least 18 moons. Two of these moons—Janus and Epimetheus—trade orbits every two years (see Figure 1).
Uranus:	Uranus, like Venus, rotates in a counter-clockwise direction (retrograde rotation). Uranus is unique in that it is tipped 98o on its axis (See Fig.2). Uranus has a magnetic field that is as strong as Earth’s Uranus has a thick atmosphere of methane, ammonia, and acetylene Uranus seems to have as many as 21 moons—perhaps the most of any planet in our solar system
Neptune:	Neptune takes almost 165 Earth-years to travel around the sun. Neptune may have rings that may rotate in pieces. Neptune has at least 8 moons. One of these moons, named Nereid, revolves in a counter-clockwise direction (see Fig. 3).
Pluto:	A year on Pluto is 248 Earth-years. Pluto, which was discovered around 1930, is usually the farthest planet from the sun in our solar system, but its revolution intersects with Neptune’s so that, at times, Neptune is the farthest planet. Pluto and Charon
	Pluto is probably covered with frozen, icy gases and the surface temperature is around -380oF. Pluto has one moon (Charon), which is one-sixth the size of Pluto. Together they revolve around the sun in an orbit that is inclined 120o from the other planet’s orbits. There is a theory that Pluto is an escaped moon of Neptune.