Eris

Eris is the largest know dwarf planet in our solar-system. It is also one of the first 3 objects categorized as a 'dwarf planet', with Pluto & Ceres. Eris was first recognized in January 2005. Some astronomers called Eris our "tenth planet" when it was first discovered (in 2003 by Michael Brown, Chad Trujillo, and David Rabinowitz). But after discussions, they decided to have a new category for objects like Eris. It is similar to Pluto, because it is a large sphere of ice & rock.

The temporary name of Eris was "2003 UB(313)", because 2003 was the year they first discovered Eris, and then nicknamed "Xena" before it was called Eris. Eris has a moon called Dysnomia. Before that, it also had a nickname -> "Gabrielle".

The diameter of Eris is about 2,500 km (1,553 miles - a little bit bigger than Pluto), but we can't be sure of it's exact size, because it is too far to see clearly, even with the world's best telescopes!

Here is a picture, so you can see the position of Eris:

Eris' orbit is not like the orbit of other planets or dwarf planets, because its orbit is like a flattened circle. Eris takes 557 years to fully orbit the Sun just once! The surface temperature on Eris is about -250°C..! Cold, isn't it?