When Pluto was first discovered, it was considered one of the 9 planets in the solar system. However, when astronomers discovered that there are other celestial bodies that have larger masses than Pluto, it was reclassified as a dwarf planet. Pluto is the 2nd most massive dwarf planet in the solar system, and it is the 10th largest object that orbits the sun.
General Information about Pluto
Pluto has a diameter of 2,390 km and a mass of 12.5 x 10²¹ kg, which is one fifth the size of our moon. It takes 6.387 days to complete one rotation and 248 years to make one revolution around the sun. The density of the planet is 1.8 to 2.1 grams per cm³, and 50% to 75% of its surface is made up of a mixture of rock and ices. Its surface temperature ranges from 40K to 50K (or -387º F to -369° F). Pluto is a very eccentric planet in that it has a highly-inclined tilt of axis and orbital path. Its tilt of axis is about 123°, and its distance from the sun ranges from 29.66 AU to 49.31 AU, meaning that it will be closer to the sun than Neptune for 20 years of its orbiting period.
For complete information and statistics on Pluto, you can go to:
- Nine Planets – Pluto: Complete information about Pluto
- ThinkQuest Info on Pluto: Provides a brief introduction, statistics, and images of Pluto.
- The Internet Encyclopedia of Science – Pluto: Comprehensive information and statistics on Pluto.
History of Pluto
Before the discovery of Pluto, astronomers observed that the orbits of Neptune and Uranus were not as circular as they were supposed to be. They suspected that another planet may be disrupting the planets’ orbiting paths. The Lowell Observatory started a project to search for the 9th planet. It was in the year 1930 that Clyde Tombaugh made the discovery of Pluto. The name ‘Pluto’ was taken from the Roman guardian of the Underworld. Pluto was regarded as the 9th planet of the solar system for a long time, but in 2006, astronomers started debating whether it should be classified as a planet or not. While it satisfies 2 of the main conditions for a celestial object to be considered a planet, it fails to meet the final condition, which states that a planet should clear the neighborhood around its orbit. Therefore, Pluto is now classified as a dwarf planet.
Information on the history of Pluto can be found at:
- PlutoPetition.com: History of Pluto and discussion on its classification as a dwarf planet.
- Planetary Glyphs and Symbolism: Explanation of the symbols of Pluto and other planets.
The Moons of Pluto
Pluto has 3 moons, namely, Charon, Nix, and Hydra. The largest moon is Charon, which has a diameter that is half of Pluto’s. Because Charon’s size is so close to its primary, the Pluto-Charon system is sometimes referred to as a double planet. One distinctive characteristic of the relationship between Pluto and Charon is that they are locked tidally, meaning that they always face each other with the same side. Charon was discovered on the 22nd of June, 1978 by James Christy. Hydra and Nix were discovered in the year 2005, but not much is known about these two moons.
Information about Pluto’s moons is available at:
- Bob the Alien’s Tour of the Solar System – Pluto: Comprehensive information about the moons of Pluto.
- History of the Pluto-Charon System: An account of the history of Pluto and Charon.
For images of Pluto, you can visit:
- Pluto Pictures Gallery: Gallery of images of Pluto.
- Pluto Gravity: Image of Pluto and Charon, and gravity calculations.
- Your Weight on Other Worlds: Images of planets and your weight measurements on each planet.
Currently, there is not enough information available for astronomers to make definite conclusions about certain aspects of the planet Pluto. However, with the arrival of the New Horizons spacecraft in July, 2015, a better understanding of the characteristics of the planet will be achieved.
