Your school books will soon have to be re-written, as scientists have given a name to a newly discovered world.
Eris, a so-called dwarf planet, lies beyond Pluto in the far reaches of the solar system, and has been causing trouble since it was found in 2005.
Some scientists said tiny Eris wasn't a real planet, but that would mean the even smaller Pluto wasn't either. So both were re-named dwarf planets.
Eris was unsurprisingly named after the greek goddess of trouble and arguments.
Facts about Eris
First seen in 2003 but finally recognised in 2005
Orbit like a flattened circle around Sun lasting 560 years
At the moment is about 14.5 billion km from Earth
Has very cold surface temperature of -250C
May have thin atmosphere when closest to Sun
Has a small moon now called Dysnomia
Eris was originally called Xena as a codename before a final name was decided.
Because it's so small and so far away, it's difficult to tell exactly how big it is.
One team of scientists think it is 70km wider than Pluto, while another think it is 700km bigger.
Eris' moon has a name too - Dysnomia, the daughter of Eris known as the spirit of lawlessness.
And Eris' troublesome nature is still causing problems - a band of scientists are now campaigning to get Pluto called a planet once more.