Rogue Planet

A rouge planet is when a planetary-mass object doesn't orbit a star, infact it orbits the galaxy itself at incredibly fast speeds, why this occurs is from this reason, the planet might have been ejected while it's solar system was forming due to it not being gravitationally bound to a star or brown dwarf. Since they planet's are moving at incredibly fast speeds if one where to hit the Earth it could create a second moon, like the collision 4.51 Billion years ago, where Theia (A Mars sized planet) had hit Gaia (Early Earth) which scientists think created the moon.