Pluto is named after the Roman god of the underworld and is on average, more than 3.6 billion miles away from the sun.

Pluto is in a region called the Kuiper Belt which contains thousands of small, icy objects like itself. Pluto was discovered in 1930 by an American amateur astronomer, Clay Tombaugh. He predicted a planet beyond Neptune, based on the motions of Uranus and Neptune. Tombaugh carried out many hours of work painstakingly comparing photos of the same area of space at different times trying to detect a planet. On February 18, 1930 he discovered such a movement and thus the ninth planet was discovered.

Pluto is much smaller than early estimates had suggested. It was not only the smallest planet in the solar system at 1,473 miles wide, it is even smaller than the Earth’s moon.  Because it is so small, many scientists don’t consider it a planet at all and on August 24, 2006, Pluto’s status was officially changed from planet to dwarf planet. A dwarf planet orbits the sun just like other planets, but it is smaller and cannot clear other objects out of its path.

Pluto has never been visited by a probe but given its distance from the sun, it should be very, very cold. NASA estimates the temperatures on its surface are about 375 to 400 degrees below zero. It is very likely covered in ice made mostly of nitrogen, with some methane and traces of carbon monoxide. When Pluto makes its closest approach to the sun, inside the orbit of Neptune, the ice on the surface may melt and evaporate thickening it’s atmosphere.

Pluto has 4 moons. The largest is named Charon. Charon was discovered in 1978 and is only slightly smaller than Pluto. For this reason, Pluto and Charon are often called a double planet system. Moreover, not only is Charon tidally locked to Pluto, but Pluto was the only planet tidally locked to its moon.

In 2006, NASA launched the first ever spacecraft mission to Pluto called New Horizons. The craft is due to arrive in 2015 after 10 years and more than 3 billion miles. New Horizons will shed a new light on the dwarf planet. Starting in in January 2015, the craft will start an intensive campaign of photography using the Long Range Reconnaissance Imager. This will help mission controllers pinpoint Pluto´s location, which is uncertain by a few thousand miles. By Spring 2015, the approaching spacecraft will be taking the closest and most detailed pictures of Pluto that surpass anything from Hubble. By closest approach in July 2015, a whole new world will open up to the spacecraft´s camera. The mission will spend more than five months studying Pluto and its moons.

Pluto Facts

  • If it were closer to the Sun, Pluto would be a comet
  • For some of it orbital period, Pluto is closer to the Sun than Neptune