By 2020, the atmospheric gases of Pluto will once again be frozen to the surface of the planet as it makes its way away from the Sun and will stay that way for more than a century. The long slugish seasons of the planet are due to Pluto’s 248 year orbit. For 20 years of Pluto’s orbit, the planet is actually the eighth planet from the Sun as it passes by Neptune’s orbit. Right now Pluto is ranked the eighth planet, but will only be there for a short time because in 1999 Neptune will regain its rank. Although Pluto may look like it passes through Neptunes path, it is actually millions of kilometers away.
At Pluto’s minimum distance from the Sun, the Sun still only looks like the head of a straight pin held away at arms length. But even at this great distance the Sun is still able to light up the planet's surface more than 600 times more brightly than our Moon does at night.
Pluto is the only planet in our Solar System that has not been examined close-up by a spaceprobe. We do know that Pluto is the smallest planet in the system. Pluto’s diameter is only 2,320 km (1,440 mi), less than 1/5 that of Earth.
Pluto was discovered in 1930 and was once thought to be one of Neptune’s Moons. But this idea is considered now to be highly improbable.
Pluto has one moon, Charon that was discovered in 1978 and has a diameter slightly larger than that of Pluto.