By Gabby Tarantino

What is a planet? We've been asking that question at least since Greek astronomers came up with the word to describe the bright points of light that seemed to wander among fixed stars. Our solar system's planet count has soared as high as 15 before it was decided that some discoveries were different and should be called asteroids.

Because Pluto and Charon are so small and far away, they are extremely difficult to observe from Earth. In the late 1980s, Pluto and Charon passed in front of each other repeatedly for several years. Observations of these rare events allowed astronomers to make rudimentary maps of each body showing areas of relative brightness and darkness.

Pluto has a very large moon that is almost half its size named Charon, which was discovered in This moon is so big that Pluto and Charon are sometimes referred to as a double dwarf planet system. The distance between them is 19,640 km (12,200 miles).

Pluto is the only world named by an 11- year-old girl. In 1930, Venetia Burney of Oxford, England, suggested to her grandfather that the new discovery be named for the Roman god the underworld. He forwarded the name to the Lowell Observatory and it was selected. Pluto's moons are named for other mythological figures associated with the underworld. Charon is named for the river Styx boatman who ferries souls in the underworld; Nix is named for the mother of Charon, who is also the goddess of darkness and night and Hydra is named for the nine-headed serpent that guards the underworld

Pluto, which was discovered in 1930, is but a dot of light in even the largest Earth- based telescopes. Pluto is 2/3 the size of Earth's moon but 1,200 times farther away, which makes viewing surface detail as difficult as trying to read the printing on a golf ball located thirty-three miles away The adjacent movie made from recent Hubble Space Telescope computer enhanced images indicates that we are finally beginning to resolve some detail on the surface of this distant planet

This, and other peculiar aspects of Pluto's orbit, have led to some speculation that Pluto is not really a planet but instead an escaped moon of one of the gas giant planets, most likely Neptune. Its composition, as inferred from its density of 2.1 g/cc, is largely ices. Thus, Pluto is more similar in structure to moons of the gas giant planets than it is to the terrestrial planets. However, other details may favor an origin of Pluto independent of Neptune, so this is an open question at present

Pluto is about 1,413 miles (2274 km) in diameter. This is about 1/5 the diameter of the Earth. Pluto is smaller than the 8 planets in our Solar System.

Pluto is 39 times farther from than the sun than the Earth is. Pluto ranges from 2.8 to 4.6 billion miles (4.447 billion to 7.38 billion km) from the Sun. From Pluto, the sun would look like a tiny dot in the sky.

Not much is known about Pluto's atmosphere. It is probably mostly nitrogen with a little carbon monoxide and methane - definitely not breatheable by humans. The atmospheric pressure is probably very low. The atmosphere forms when Pluto is closest to the Sun and the frozen methane is vaporized by the solar heat. When it is farther from the Sun, the methane freezes again. From Pluto, the sky would appear black, even when the Sun (the size of a star) is up.

Even though Pluto is a dwarf planet, and no longer officially a planet, it’ll still be a fascinating target for study. And that’s why NASA has sent their New Horizons spacecraft off to visit it. New Horizons will reach Pluto in July 2015, and capture the first close-up images of the (dwarf) planet’s

After a year of observations, Tombaugh finally discovered an object in the right orbit, and declared that he had discovered Planet X. Because they had discovered it, the Lowell team were allowed to name it. They settled on Pluto, a name suggested by an 11-year old school girl in Oxford, England (no, it wasn’t named after the Disney character, but the Roman god of the underworld)