The characteristics that the outer planets have in common include their large size and their large number of moons when compared with the inner, or terrestrial, planets. They also lack solid surfaces, and as far as astronomers know, none are capable of supporting life. For example: Jupiter and Saturn are "gas giants" with atmospheres made up largely of hydrogen and helium, while Neptune and Uranus are called "ice giants" because their atmospheres also contain ammonia, methane and water ices.Continue Reading
One reason that the outer planets can't support life is that their "surfaces" are extremely cold. The temperature of Saturn is -288 degrees Fahrenheit, while the temperature of Jupiter is -244 degrees. The surface temperature of Neptune is -330 degrees, and the surface temperature of Uranus is -323 degrees.
Compounding the low temperatures of the outer planets are areas of brutal winds. Winds on Uranus can attain speeds of 240 miles per second, but Neptune has the fastest sustained winds of all the planets, with speeds clocked at 1,300 miles per hour.
The planets also have rings. Although Saturn's rings are the most spectacular, the other three also have ring systems. The outer planets are also believed to have solid, rocky, metallic cores.Learn more about Planets