Pluto's mass is about 1.29 x 1022 kg. This is about 1/500th of the mass of the Earth. The gravity on Pluto is 8% of the gravity on Earth. A 100 pound person on Pluto would weigh only 8 pounds. Each day on Pluto takes 6.39 Earth days. Each year on Pluto takes 247.7 Earth years (that is, it takes 247.7 Earth years for Pluto to orbit the Sun once).
In 2006, NASA launched the first mission to Pluto. It is called New Horizons. New Horizons is a spacecraft that is going to the edge of the solar system. The spacecraft is about the size of a piano. It will take nine years to reach Pluto. In 2015, New Horizons will arrive at Pluto. The mission will spend more than five months studying Pluto and its moons. New Horizons will then study other objects in the Kuiper Belt. New Horizons has cameras that will take pictures of Pluto. The spacecraft also has science tools to gather information about Pluto. These pictures and information will help scientists learn more about the dwarf planet.
The Hubble Space Telescope has provided the clearest images yet of this dwarf planet for scientists to study. Studies of Pluto and its moon are still being conducted today with the Hubble Space Telescope. However, little is still known about Pluto and its moons because it is so far away.
According to the new definition, a full-fledged planet is an object that orbits the sun and is large enough to have become round due to the force of its own gravity. In addition, a planet has to dominate the neighborhood around its orbit. Pluto has been demoted because it does not dominate its neighborhood. Charon, its large "moon," is only about half the size of Pluto, while all the true planets are far larger than their moons. In addition, bodies that dominate their neighborhoods, "sweep up" asteroids, comets, and other debris, clearing a path along their orbits. By contrast, Pluto's orbit is somewhat untidy.
On August 24, 2006, the International Astronomical Union (IAU), an organization of professional astronomers, passed two resolutions that collectively revoked Pluto's planetary status. The first of these resolutions is Resolution 5A, which defines the word "planet." Another resolution, Resolution 6A, also specifically addresses Pluto, naming it as a dwarf planet. Not all astronomers support Resolutions 5A and 6A. Critics have pointed out that using the term "dwarf planet" to describe objects that are by definition not planets is confusing and even misleading. Some astronomers have also questioned the resolutions' validity, since relatively few professional astronomers had the ability or opportunity to vote.
After the discovery of Pluto, it was quickly determined that Pluto was too small to account for the discrepancies in the orbits of the other planets. The search for Planet X continued but nothing was found. Nor is it likely that it ever will be: the discrepancies vanish if the mass of Neptune determined from the Voyager 2 encounter with Neptune is used. There is no Planet X. But that doesn't mean there aren't other objects out there, only that there isn't a relatively large and close one like Planet X was assumed to be. In fact, we now know that there are a very large number of small objects in the Kuiper Belt beyond the orbit of Neptune, some roughly the same size as Pluto.
Discovered in 1930, Pluto was long considered our solar system's ninth planet. But after the discovery of similar intriguing worlds deeper in the distant Kuiper Belt, icy Pluto was reclassified as a dwarf planet. This new class of worlds may offer some of the best evidence about the origins of our solar system. Pluto is also a member of a group of objects that orbit in a disc-like zone beyond the orbit of Neptune called the Kuiper Belt. This distant realm is populated with thousands of miniature icy worlds, which formed early in the history of our solar system. These icy, rocky bodies are called Kuiper Belt objects or transneptunian objects.
Pluto is the only world named by an 11-year-old girl, Venetia Burney of Oxford, England, who suggested to her grandfather that it get its name from the Roman god of the underworld. Her grandfather then passed the name on to Lowell Observatory. The name also honors Percival Lowell, whose initials are the first two letters of Pluto.
Ptolemy was a Greek astronomer who lived from A.D. 100 to 179. He was one of the first to describe how planets "wander." Ptolemy said planets moved in an orbit, a curved path that one object travels along as it revolved around another.
Pluto is a spherical object composed of rock and ice, but mostly ice, located on average almost 6 billion km (4 billion miles) from the Sun. In comparison, Earth is a ball composed of mostly rock, located forty times closer to the Sun than Pluto, at an average distance of only 150 million km from the sun. Pluto's diameter is .19 (or 19 percent) times the diameter of the Earth which is 12,756 km at the equator.