Pluto - The Dwarf Planet

Updated: Apr 10, 2019


“Are you old enough to remember when Pluto was a planet?”





The story of Pluto starts in 1930, when an amateur astronomer, the American Clyde Tombaugh, who was hired to expose photographic plates with his new camera by night, discovered a small planet - what he noticed, at last, was a tiny spot of light moving slowly against the fixed pattern of stars in the constellation Gemini. That remote object was a suspected planet, Pluto. Funnily, the name, Pluto: the Roman god of the Underworld, who was able to render himself invisible, came from an 11-year-old English girl and both the American Astronomical Society and the UK’s Royal Astronomical Society accepted it immediately.





Until 2006, Pluto was considered as the ninth planet in our solar system, but since then people do not have to bother with remembering its name when it comes to planets in our solar system. During the meeting of the International Astronomical Union, Pluto was labeled as a dwarf planet. According to the agreements an object has to meet three criterions to be regarded as a planet. First it has to revolve around its star – so in the case of Pluto, it is the Sun, approximately has a spherical shape – which means that it’s big enough, has its own gravity and lastly, it has to sweep the path in front of itself. These clarifications were needed as planets with greater mass, such as Eris, were found in the Kuiper belt, the area beyond Neptune. The 2 possible solutions were naming Pluto and all the newly found planets dwarf planets or announcing that our solar system has a lot more members.

Many debate these ideas. The American Philip Metzger states that the one and only criteria when we classify an object should be its size. Active geological processes are enabled once the planet is big enough to have a spherical shape. For instance, Pluto has an underground ocean, atmosphere, geological formations, and moons. A significant portion of its mass is icy material (such as frozen water, carbon dioxide, molecular nitrogen, methane, and carbon monoxide).


Pluto is a really special planet at the edge of our solar system. Despite it is considered as a dwarf planet that doesn’t make it any less from the others and holds a lot of new surprises for the curious minds. I am old enough to remember when Pluto was called a planet and for me, there will always be a planet after Neptune.






Written by: Rebeka Oláh


Rebeka Oláh is the Board Member for Voyager Space Outreach for writing Blog posts on STEM/Space Topics.

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