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Pluto is largest and second most-massive dwarf planet located in the outer solar system, in an area known as the Kuiper Belt. It was first discovered in 1930 and was considered a planet until 2006, when it was downgraded to dwarf. It is primarily made of ice and rock. It is notable for the controversy regarding its demotion and the resulting online fandom.
On August 24, 2006, the International Astronomical Union (IAU) defined what it means to be a "planet" within the Solar System. This definition excluded Pluto as a planet and added it as a member of the new category "dwarf planet", along with two other celestial bodies, Eris and its moon Dysnomia. This event sparked protests, both online and off.
Usenet discussion in the group alt.planets.pluto increased during this time and several online and offline petitions began to circulate to return Pluto to planet status, and the Society for the Preservation of Pluto as a Planet was founded. Alan Stern, the head scientist of the New Horizons mission to visit Pluto, was one of the most vocal advocates of reinstatement, calling Pluto's demotion "sloppy." In 2008, the IAU decided that instead of reclassifying Pluto as a full planet, it would instead be referred to as a "Plutoid" body.
The verb "to pluto" (preterite and past participle: "plutoed") was a neologism coined in the aftermath of its transition from planet to dwarf planet in the aftermath of the 2006 IAU decision. In January 2007, the American Dialect Society chose "plutoed" as its 2006 Word of the Year, defining "to pluto" as "to demote or devalue someone or something", "as happened to the former planet Pluto when the General Assembly of the International Astronomical Union decided Pluto no longer met its definition of a planet."
New Horizons Mission
On January 19th, 2006, the New Horizons spacecraft was launched with the express mission "to study Pluto, its moons and the Kuiper Belt, performing flybys of the Pluto system and one or more Kuiper Belt Objects (KBOs)," including taking the first detailed mapping photographs of the distant mass. It is the fastest craft ever built by NASA.
It was originally meant to be part of a larger mission for exploring the outer reaches of the solar system, but with declining funding for NASA, the New Horizons mission eventually became a sole craft. The ship was expected to make its closest pass to Pluto on July 14th, 2015. On board, the ship contained the ashes of Clyde Tombaugh, the astronomer who originally discovered Pluto in 1930.
The first images of Pluto beamed back from the ship arrived on Earth on July 13th, 2015, and immediately began to spread worldwide. The photo confirmed, among other things, that the color of Pluto was a sandy red. Many online noted that the lower half of the planet, as seen in the image, looked like the Disney character Pluto, a dog. Others began to photoshop other things into the peach-colored space. Overall, reaction was massive, with almost 400,000 people tweeting about Pluto that day. More than 15 posts featuring the image received more than 3,000 upvotes on Reddit, and the photograph was posted extensively on Tumblr, where it was a trending topic.
On July 15th, NASA released more detailed photographs of the planet beamed back from the spacecraft, including revealing that one of the regions on Pluto was informally called Cthulu, and that another region on one of its moons, Charon, was referred to as Mordor. It also revealed that the dwarf planet was full of "ice mountains."
 Usenet Archive – Alt.Planets.Pluto
 Society for the Preservation of Pluto as a Planet
 American Dialect Society – “Plutoed” Voted 2006 Word of the Year
 The Atlantic – What's So Great About Being a Planet?
 Wikipedia – New Horizons
 Reddit – TIL the New Horizons space probe, which is scheduled to reach Pluto in July 2015, has on board the ashes of Clyde Tombaugh, who discovered the planet in 1930.
 Topsy – Pluto + New Horizons
 Reddit – Search: Pluto
 New York Times – New Horizons Reveals Ice Mountains on Pluto
 Motherboard – New Horizons Is Finally Close Enough to Confirm That Pluto Is Red
Jul 15, 2015 at 06:55PM EDT
Jul 15, 2015 at 06:03PM EDT
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