Pluto, formerly the ninth planet in our solar system, and now dwarf planet “134340 Pluto” now, has seen some ups and downs throughout its known history. Now the little wannabe planet will be in the news again as it vies for a potential comeback.
The existence of a ninth planet was predicted since the 1800s, as its presence was required to explain discrepancies in the orbits of other planets. The actual planet itself was not discovered until 1930 by amateur astronomer Clyde Tombaugh. The name for Pluto was suggested by an 11 year old English girl named Venetia Burney. In 1978 it was discovered, by James Christy, an astronomer at the US Naval Observatory, that the little planet had its own moon, subsequently named Charon. While originally estimated to be the same size as our own planet, Pluto has been calculated to be only 1% the mass of Earth.
The discovery of other giant ice bodies in the vicinity of Pluto, now dubbed the Kuiper Belt, led to the discussion in 1999 of whether Pluto should be designated as a planet and as a minor planet. The idea was proposed by the International Astronomical Association’s Minor Planet Center, but they soon abandoned the idea.
In 2005 the planetary body Eris was discovered by Michael E. Brown of the California Institute of Technology (it was originally named Xena by Brown). Eris was calculated to be larger than Pluto, which presented a problem. Astronomers would either have to add Eris as a tenth planet or drop Eris and Pluto from planetary status. In 2006 the term dwarf planet was created by the International Astronomical Union, meaning that it is large enough that its own gravity causes it to form into a round shape, but it is not the gravitationally dominant object in its orbit.
Fast forward to November 2010, when Eris passed in front of a distant star, allowing astronomers to achieve a more accurate measure of its size, and it turns out it is actually smaller than Pluto. So now the important questions are, should Pluto have been demoted, should there still be nine planets in our solar system, and how accurate are these measurements?
The last question is probably the most important as the precise diameters of Pluto and Eris have been under debate since their respective discoveries, so only time will tell.
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