The International Astronomical Union (IAU) met in August, 2006, and voted on the first official definition of a "planet," and because of that definition, Pluto is no longer considered a planet. Pluto will now be known as a dwarf planet, one of several in our solar system.

     The new official definition of a planet is: a celestial body that is in orbit around the sun, has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a nearly round shape, and has cleared the neighborhood around its orbit. That means, more simply, that to be a planet, an object must be spherical, and does not cross other planets' paths in its orbit. Pluto crosses the orbit of Neptune every 228 years, for twenty years. For those twenty years, Pluto is closer to the sun than Neptune.

     We now know that there are many large icy objects, called Kuiper Belt Objects, found on the fringes of our Solar System. The discovery of 2003UB313, now called Eris, which is larger than Pluto, made astronomers question once again whether Pluto is really a planet.

• Pluto was once considered the smallest and coldest planet in our solar system, with temperatures reaching 382 degrees below zero!
• It was discovered by Tombaugh in 1930.
• It was the only planet not visited by a spacecraft. The New Horizons spacecraft lifted off on January 19th, 2006, hoping to approach Pluto on July 14, 2015.
• Some believe that Pluto might be an escaped moon of Neptune because it is like Neptune's moon, Triton.
• Pluto is unlike the other outer planets because it is not gaseous. Scientists think it is an ice ball of methane gas and water mixed with rock and  that its thin atmosphere is mostly nitrogen and methane. 
• Its orbit is highly elliptical and also tilted 17 degrees.
• Pluto is slightly smaller than our own moon, about 1,800 miles across.
• It has three known moons, one of which, Charon, is only 12,400 miles from Pluto and half as wide. It was discovered in 1978.
• Two new moons were discovered late in 2005, and were named Nix and Hydra in 2006.
• Pluto, like Uranus, lies on its side, but not quite as much.
• It takes 17 years for light from the Sun to reach Pluto.
• Seeing what is on the surface of Pluto is like trying to read the printing on a golf ball which is 33 miles away.
• The speed that a planet travels around the Sun depends on how close it is to the Sun. Since Pluto is very far away, it moves very slowly, about three miles a second. It takes 248 of Earth years to travel one time around the Sun. A day on Pluto would last about 6 1/2 Earth days.
• It is very possible that Pluto has rings that formed at the same time as its three known moons.
• NASA released the New Horizons mission on January 19, 2006, that is due to visit Pluto in ten years.