Pluto was, at one time, the ninth and “furthest” planet away from the sun, orbiting in what is known as the Kuiper Belt. Because of how far away Pluto is, we do not have as much information about it as we do with most of the other planets in the solar system. Pluto was named by Venetia Burney, an 11-year-old from England, who suggested the name based on the Roman god of the underworld. We believe that it has an estimated diameter less than one-fifth that of Earth or only about two-thirds as wide as Earth’s moon. It most likely has a rocky core, with a mantle of water ice, while containing methane and nitrogen frost on its surface. The Hubble Space Telescope showed that Pluto’s crust could contain complex organic molecules, which are the building blocks of life. It has also returned images showing that Pluto is reddish, yellowish and greyish in different areas. Pluto has a very eccentric orbit, and at times can be closer to the sun than Neptune. When this happens, some of the surface ice on Pluto can thaw out and create an atmosphere, but then freezes and disappears as Pluto moves further away from the sun, because of temperatures reaching -225 degrees Celsius. It has an orbital period of 248 earth years, but is closer to the sun than Neptune is for 20 of those years. Pluto has 5 known moons, it’s largest moon being Charon. Charon is almost half the size of Pluto and experiences the same tidal locking as Earth and its moon. Pluto’s other 4 moons, Nix, Hydra, Kerberos, and Styx are all very small ranging in sizes between 13-100 km wide. Another interesting property about Pluto is that its orbit is tilted 17 degrees relative to the rest of the solar system, unlike the rest of the planets that stay close to the plane of the solar system.
Pluto was discovered by Clyde Tombaugh, on February 18, 1930. Tombaugh used a telescope that had a camera that took pictures of the sky on different days. He then used a blink compactor (comparator) which flips between the pictures, allowing him to compare the two pictures and look for any objects that showed any motion between the pictures. This is how Pluto was discovered.
Clyde Tombaugh was born on February 4, 1906, in Illinois. He constructed his own telescopes throughout his life, completing his first one at the age of 20. He used these to make more detailed observations of Mars and Jupiter, and sent these observations to Lowell Observatory, where he would be offered a job to operate their new telescope. This is where he would later discover Pluto. In World War II, he taught navigation to the U.S Navy at Arizona State College, and later worked at the ballistics research lab at White Sands Missile Range in New Mexico. He would also catalog over 30 000 celestial objects throughout his life. He died on Jan 17, 1999, in New Mexico.
The American astronomer Percival Lowell, is where the search for another planet beyond Neptune began. He studied the orbits of Uranus and Neptune, and noticed irregularities which he determined were caused by a planet beyond Neptune. He predicted a probable location of the planet and organized a search for the planet in 1915. This eventually lead to Tombaugh getting a job at the Observatory, as mentioned earlier, and becoming part of the search 13 years later. While there was an organized search for Pluto and there was a prediction on its possible location, it is a little difficult to say that it was found based on theoretical predictions. Unlike Neptune, which was found very quickly after calculating its predicted location, Pluto was not found until 1930. 15 years after Lowell had made a prediction about its location. On the other hand, it was calculations of the orbits of Uranus and Neptune that lead to the search for Pluto in the first place, so Pluto’s discovery was not entirely luck based either.
Pluto has sparked interesting debates since its discovery in 1930. When Charon was discovered in 1978, it was determined that Pluto was not actually as large as first thought because of how close Charon is to Pluto and the size of Charon, in relation to Pluto. As mentioned earlier, Pluto has an atmosphere as it gets closer to the Sun, but loses that atmosphere as it moves further away. Pluto’s biggest debate is its reclassification as a dwarf planet. With objects such as Ceres, Eris (discovered in 2003), and other Trans-Neptunian objects found, The (IAU) International Astronomical Union, had to redefine what a “planet” was. After gathering information and opinion from multiple sources such as “professional astronomers, planetary scientists, historians, science publishers, writers and educators”, the IAU redefined what a planet is, and Pluto did not match the criteria. In 2006, Pluto was reclassified as a dwarf planet, after it was considered as the ninth planet since its discovery.
A plutino is a trans-Neptunian object, that has the same orbital period as Pluto, and also has the same 2:3 orbital resonance with Neptune that Pluto has. They are basically large icy bodies that lie beyond the orbit of Neptune, in a region known as the Kuiper Belt. While Pluto and Eris are two of the larger known objects in this region, there are hundreds of objects within the Kuiper Belt that share these properties, and can also be considered as plutinos as well.