The Auriga was a United Systems Military research vessel stationed in unregulated space just outside the orbit of Pluto. It housed laboratories that were used by Dr. Mason Wren and his team to clone Ellen Ripley for the alien queen inside her in 2385. These same laboratories were then used by the scientists to breed Xenomorphs for the United Systems Military's bioweapons plan.
When multiple aliens broke from their holding cells on the Auriga, it was evacuated by General Perez, and then, per standard procedure, auto-piloted itself back to Earth. The Auriga crashed into the atmosphere above Africa, destroying the ship, when Ripley and the surviving crew of the Betty purposefully rigged it to do so with the intent of destroying all the Xenomorphs aboard.