It’s Almost Twenty Years Since The ‘Justice For Pluto’ Movement Began, And Here Is Exactly Why The Dwarf Planet’s Reclassification Happened
2005. The year that YouTube was launched, The US Office and The Suite Life Of Zack And Cody premiered, a new Pope was inaugurated, and Canada became the fourth country in the world to officially allow same-sex marriage.
And it was also the year that a discovery was made, one year on culminating in Pluto being stripped of its planetary status.
Cue outcries in the media and on fledgling social media sites alike. There was a lot of sadness when what was formerly known as the smallest planet in our solar system was reclassified, with “Justice for Pluto” movements sweeping the internet.
So why, twenty years ago, did this tiny planet become known in entirely different terms?
Well it was all down to an important discovery by a team of astronomers.
On January 5th, 2005, a research team discovered a new dwarf planet, which was ultimately named Eris.
Due to its size, Eris was an important, newly-discovered player in our solar system. The key message was that Eris was bigger than the dwarf planet that had, until that time, taken last place in our planetary line-up.
Though it is orbited by five moons, according to NASA Pluto is only around 1,400 miles wide – or half the width of the US.
This shook everything that we knew about our solar system, leading to controversial discussion about whether or not Eris should be included in our classifications, or whether knowledge of this new dwarf planet meant that Pluto was now to head down a different path and join a new grouping altogether.
So why was the latter option chosen?
Because soon after, other dwarf planets were discovered too. Our technology had improved to such an extent that a whole group of new dwarf planets were identified, taking the new planet count up to five. This caused a headache for space experts, who ultimately decided that Pluto should be grouped with its dwarf planet brethren, rather than keeping its planetary title.
At a meeting of the International Astronomical Union on August 24th, 2006, scientists explained that, since other dwarf planets had been discovered in a region called the Kuiper Belt, the definition of what constitutes a planet would be redefined as something that orbits its host star, is mostly round, and influences the orbital stability of other objects in space. Meanwhile, a dwarf planet does not have significant pull, as the IAU explain:
“A dwarf planet is an object in orbit around the Sun that is large enough to pull itself into a nearly round shape but has not been able to clear its orbit of debris. Generally, dwarf planets are smaller than Mercury. A dwarf planet may also orbit in a zone that has many other objects in it. For example, an object within the asteroid belt is in a zone with many other objects that are all about the same size. Pluto now falls into the dwarf planet category because it resides within a zone of other objects that might cross its orbital path, known as the Trans-Neptunian region.”
Thus, along with Pluto, other newly-discovered dwarf planets – including Eris, Ceres, Haumea, and Makemake – were inaugurated as part of this new classification.
Though it was a sad day for Pluto fans, perhaps the dwarf planet feels more at home among its counterparts.
If you thought that was interesting, you might like to read about a second giant hole has opened up on the sun’s surface. Here’s what it means.

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