Pluto

Pluto is usually the most distant of all the planets. Pluto's average distance from the sun is about 3.7 billion miles. Since Pluto is so far from the sun, its year is almost 250 Earth years long, that would be nearly two and a half centuries! Pluto's day is about six days, which isn't really long compared to Venus's rotation. Venus's rotation is about 243 Earth days. Pluto's average temperature is about -400*F. Pluto was discovered in 1930 by Clyde Tombaugh. Pluto was named after the Roman god of the underworld.

An Ice Planet

As a result of Pluto's distance, scientists have not been able to learn a lot about the planet. But studies show that Pluto is probably made of mostly ice, and its surface seems to be made up of frozen methane. Since Pluto is very cold, it is the only planet with a solid methane atmosphere.

Pluto and Its Moon, Charon

Pluto is 1400 miles in diameter, which makes it smaller than our moon. Charon however is 750 miles in diameter, slightly larger than half of Pluto. Charon is quite big for a moon with a planet the size of Pluto. That makes Pluto and Charon the closest in size of any planet-moon pair in the solar system. Charon and Pluto are very close to each other. They are only about 12,000 miles apart.

Charon's composition and other details about the moon are not yet known.

A Long Way to the Sun

Pluto is forty times farther from the sun than Earth is, but its orbit isn't circular like the other planets. Instead Pluto has an oval-shaped orbit, so its distance from the sun can change widely depending on where it is. For 20 years, Pluto's orbit intercepts with Neptune's and it becomes the eighth planet. This just happened from the year 1979 to 1999.