Traditionally we are taught in school that there are nine planets. Now, Pluto has been classified as a dwarf planet and is no longer considered as one of the “big boys.” Down graded along with Pluto is the tenth planet of the solar system. Yes, Virginia, there’s a tenth planet. The discovery of the planet wasn’t made into a big deal back in 2005 because, even then, the International Astronomical Union (IAU) was reconsidering the definition of what a planet was.

Eris was first recorded on October 21, 2003. Because of the very slow movement of the planet, it was not noticed as such. Even when the images are placed into animation, it is still very difficult to see where the planet actually is. In most cases, the observer has to be told where to look. The dwarf planet wasn’t identified until a Mount Palomar based team, led by Mike Brown, including Chad Trujillo and David Rabinowitz, noticed the moving ball on light on the images captured from 2003. On January 5, 2005, the planet was finally recorded and officially recognized. The name then given to the planet was 2003UB313. To those that were working on the research of the planet, it was given the nickname of Xena. The name Eris was later adopted, and fittingly so, for it was around this time that the uproar with Pluto being down-graded began. (Apparently that’s what you get for naming a new planet after the goddess of strife and discord.)

Fittingly it is called the tenth planet not only because of its discovery after Pluto, but also because its orbit does indeed put it past the ninth planet. This tenth planet is very similar to Pluto. Considered another Kuiper Belt Object, Eris has traits that match its dwarf planet friend. Not only is it of similar size, having a diameter of 1,550 miles (2,400 kilometers) and being only 27% larger than Pluto, but Eris is made mostly of ice. If it was brought within the distance to the sun that Earth is, it would simply melt away. Like Pluto, the majority of the ice is not composed of water, but of methane. (This in turn means that the surface temperature of the planet ranges anywhere from -243 to -217 degrees Celsius.) Because the planet is so far away from the sun, it differs from Pluto in the manner that the methane is allowed to form a uniform covering, giving it a grey color.

Like Pluto, Eris also has a moon. On September 10, 2005, roughly nine months after the initially discovery of the dwarf planet’s existence, the same team that discovered Eris was working at the Keck Observatory in Mauna Kea. Turning the most powerful telescopes on the planet, they were rewarded by finding that it had a small satellite orbiting it. The team named the moon Dysnomia, the demon spirit of lawlessness and Eris’ daughter. The size of the moon is currently unknown. Scientific estimation puts it anywhere from 100km to 250km.

While some scientists beg to argue that dwarf planets should not be considered planets at all, others claim that there needs to be room for differentiation between planet types without discrimination. No matter what the case is, Eris was found as a planet and called such at the time of its discovery. For that alone, Eris is called the 10th planet by its founders. As always, the more we discover about our solar system, the more the books need to be rewritten. At least Pluto will not be alone in its new classification.