There once was a planet that is no longer considered a planet like Earth, Mars, and the other 6 planets of the solar system. Pluto was once classified as a planet, but in 2006 the International Astronomical Union (IAU) demoted Pluto to a 'dwarf planet'. It is still thought of as a planet, but not in the same way as the other eight planets of the solar system. There are several differences, which makes Pluto no longer one of the solar system's planets. Pluto is located about 3.5 billion miles on average from the Sun
According to the IAU, Pluto is no longer a regular planet because it has not cleared its neighborhood around its orbit and it is not a considered a satellite. Pluto, though, still has a special place in the solar system for a variety of reasons. It holds keys to possible life, its atmosphere has been thoroughly studied, the climate differences caused by its distance from the Sun has been studied, and several other reasons make Pluto a unique planet to learn about. For many years Pluto was the most distant large object astronomers knew anything about, which in itself was significant and important to many astronomers.
Pluto was discovered by astronomer Clyde Tombaugh in 1930 and it takes 248 years to orbit the Sun. At times, because of the elliptical orbit of Pluto and the other planets, it is closer to the Sun than Neptune. During those years between 1979 and 1999, scientists were able to learn much more about Pluto and its very large moon, Charon, as well as its four other moons. Pluto's temperature is about 375 degrees below zero.
Pluto's name came from the Roman god of the underworld. It was suggested by an 11-year-old girl and it also honors Percival Lowell, whose initials are the first two letters of Pluto. Lowell was an astronomer who first caught a glimpse of Pluto's existence in 1905, and predicted the planet's existence but died before he ever found it.
Scientists still want to learn much more about Pluto and other far away areas of the solar system, so a robotic space flight mission was launched in 2007. NASA sent an unmanned mission called New Horizons taking eight years to arrive on the dwarf planet. It has allowed the study of Pluto and other areas in the region.
The New Horizons mission discovered that Pluto has a diameter of 1,473 miles, less than 1/5 of the Earth's diameter, and only about 2/3 of the width of the Earth's moon. It also noted surface features that included mountains as high as 11,000 feet, which are comparable to the Rocky Mountains on Earth. The scientists believe the mountains are formed on a bedrock of water ice. The mission also sent back many other new observations of Pluto such as it not having craters, meaning the planet is very young at about 100 million years old. It was also revealed that Pluto may have regular seasons based on the color of the planet's surface changing over time.
In summary, Pluto is no longer the ninth planet of the solar system, but it is still a planet called the dwarf planet. It was first noticed in 1905 but was not discovered as a planet until 1930. The planet has significant value to scientists and astronomers because everything learned about the distant planet will also help answer questions about how the planet Earth works.