Let's rewind. 1930, Clyde Tombaugh discovered the
dwarf planet Pluto. That's like...not that long ago. I seriously thought Pluto was discovered way before that. 2005, Mike Brown discovers an object 27% greater than that of Pluto with an orbit around the sun. Pluto is now what we call a dwarf planet. A dwarf planet is just massive enough for it's shape to be controlled by gravitation and orbit the sun. Unlike a planet, a dwarf planet hasn't cleared it's orbital region of other objects. Other objects such as the one Mike Brown discovered perhaps? Eris. I don't know honestly, I just know that's the name of the dwarf planet found giving away Pluto. Ruining everything, like a total bitch.
According to Star (HA), the two - Pluto and Eris - are happy they've found one another.
If I got you into a science mood, I highly suggest YouTube-ing a bunch of BillNye, and if you have Netflix watch some Breaking Bad.