136199 eris, known before as 2003 ub 313, is a dwarf planet and a trans-neptunian object (also known as tno) in the solar system. it is the largest dwarf planet known so far, and it is bigger than pluto. it was discovered by michael e. brown, chad trujillo, and david rabinowitz on january 5, 2005, when they had a close look at some old images of the outer solar system that were taken in 2003. eris was firstly known as xena, named after the main character of the television series xena: warrior princess. eris has one companion moon called dysnomia, also known before as 2003 ub 313, discovered on september 10, 2005.
