Lua

Lua was a huge asteroid which collided with Ru, the home planet of the Ru'Harem. The collision destroyed the planet, splitting it clean into two pieces. These "pieces" later formed into two new planets, Ru'un and Earth, which somehow remained in orbit around the Sun.

The collision was predicted by the Ru'Harem who had already evacuated their homeworld beforehand. After their return to the system it was speculated that debris from Lua may be responsible for the formation of moons around both new planets.