Pluto was discovered in 1930 by an Clyde Tombaugh, a 23-year-old Kansan at the Lowell Observatory. Analysing perturbations in the orbit of Uranus led to the discovery of Neptune but additional perturbations suggested another planet - planet X. The observatory received over 1,000 suggestions for its name from all over the world, ranging from Atlas to Zymal.
The name Pluto, after the god of the underworld, was proposed by Venetia Burney (1918–2009), an eleven-year-old schoolgirl in Oxford, England, who was interested in classical mythology. She suggested it in a conversation with her grandfather Falconer Madan, a former librarian at the University of Oxford's Bodleian Library, who passed the name to astronomy professor Herbert Hall Turner, who cabled it to colleagues in the United States
Today, Pluto is called a "dwarf planet." A dwarf planet orbits the sun just like other planets, but it is smaller. A dwarf planet is so small it cannot clear other objects out of its path.
On average, Pluto is more than 3.6 billion miles (5.8 billion kilometers) away from the sun. That is about 40 times as far from the sun as Earth. Pluto orbits the sun in an oval like a racetrack. Because of its oval orbit, Pluto is sometimes closer to the sun than at other times. At its closest point to the sun Pluto is still billions of miles away.
Pluto is only 1,400 miles (2,300 kilometers) wide. That's about half the width of the United States. Pluto is slightly smaller than Earth's moon. It takes Pluto 248 years to go around the sun. One day on Pluto is about 6 1/2 days on Earth.
The plutonium-powered New Horizons probe — roughly the size and shape of a grand piano — is heading for a flyby 6,200 miles from Pluto’s icy, unexplored surface on July 14, 2015, but observations will begin in December.
“We’re at the very tail end of this very long cruise across almost 3 billion miles of our journey from the Earth to the Pluto system,” said Alan Stern, principal investigator on the New Horizons mission . “On December 6, we’ll wake New Horizons up from its last hibernation and we will be on the doorstep of the Pluto system. Encounter starts just a few weeks later on January 15.”