Pluto was confirmed as a planet on February 18th 1930 by a young astronomer from Kansas named Clyde W. Tombaugh who was only 23 at the time. The discovery was made in the Lowell observatory in Arizona where he carried out his research. There had long been predicted that there was a 9th planet dubbed planet X due to perturbations in the orbit of the then furthest away planet Neptune.

Pluto was discovered by systematically taking fortnightly images of particular celestial coordinates in the night sky where this planet X was likely to be. These images would then be put through a machine called a blink comparator which would run through the images quickly to see if any of the objects had shifted in position. By examining pictures taken on the 23rd and the 29th of January Tombaugh and his colleges at the Lowell observatory were able to confirm they had discovered planet X which to this day is known as Pluto. On March 13th 1930 the news of the discovery was telegraphed to the Harvard College Observatory and was made public.

Pluto has a diameter of 2274 km, orbits at an average of 39.5 AU away from the Sun and has a mass of 1.27×10^27 kg. The current smallest planet Mercury has a diameter more than double that of Pluto (4879 km) and is much more massive with a mass of 3.30×10^23 kg making Pluto seem relatively insignificant in comparison.

However, Pluto’s orbit is very close to that of Neptune’s, currently the planet furthest away from the sun. Neptune has an average orbit of 30.1 AU away from the Sun and because Pluto can get as close as 30.5 AU, the two overlap and at times Pluto is closer to the Sun than Neptune.

Pluto has been classified as dwarf planet since 2006 after being famous to all as the ninth planet. In comparison to the smallest dwarf planet Ceres, Pluto is much larger and more massive. In fact Pluto’s moon Charon is both more massive and has a larger diameter than Ceres showing Pluto to be much more substantial than another body that is classified in the same category as it.

The Dwarf planet Pluto has many attributes that make it uniquely different to the so called planets of the solar system. Pluto spends most of its orbit in the Kuiper belt which is made up of asteroids; this is different to the planets of the solar system which do not orbit in an asteroid belt. Pluto has a very long orbital period which takes 249 earth years, this is a lot longer than the 164.8 earth years it takes for Neptune to orbit the sun. Pluto’s orbit also has a very high eccentricity meaning that its distance from the sun varies greatly during its orbit, this in turn causes it to be closer to the sun than Neptune for a brief 20 earth years during its 249 year orbit. The plane of Pluto’s orbit is also greatly tilted compared to that of Earth’s or any other planet in the solar system, this takes it further north or south of Earth’s orbital plane than any other planet in the solar system. Pluto’s moon Charon is also the largest in size compared to its mother object with a diameter of just over half that of Pluto, causing the centre of the orbit between these two objects to reside outside the surface of Pluto. Pluto breaks the cycle of gas giants which occur after Mars which includes Jupiter, Saturn, Uranus and Neptune as it has attributes more closely related to terrestrial planets such as being relatively small and solid and with fewer moons. Despite all these unique attributes Pluto had stayed classified as a planet up until 2006.

An example of Pluto being distinguishably different to other dwarf planets is its distance from the Sun. The present largest dwarf planet Eris is more than three times the distance away from the Sun with a mean orbit of 96.6 AU. Another reason that makes Eris significantly different to Pluto is the shape of its orbit. Pluto like the main 8 planets has an almost spherical orbit however Eris does not and moves around the Sun in an elliptical motion. On the other hand, if the assignment of a planet is made from the size and mass of a body then Eris has a stronger argument to be designated as a planet. It has a mass of 1.67×10^22 kg, slightly more massive and has a larger diameter of 2300 – 2400 km. Therefore if Pluto were to be classified as a planet on the grounds of its size and mass then Eris should be as well.

Pluto is found in an area of the solar system known as the Kuiper belt that contains many small bodies, mainly composed of ice. This is also where two other dwarf planets, Haumea and Makemake are found. Although they are smaller than Pluto they follow a similar orbit as they are found in the same region and have an almost spherical shape due to their gravitation. As these are found in the same region as Pluto and have these similar characteristics both Haumea and Makemake have an equal right to be described as planet. However, one of the definitions of a planet is that the body must have cleared its path of similar sized objects, therefore it is difficult for Pluto to be classified as a planet with two other dwarf planets in the same area unless the definition of a planet is changed.