Poobatron is a planet home to a peaceful race called the Poobs. They are the closest galactic neighbors of the Koozebanians, and the two races have been communicating with each other for many generations, via radio transmissions. Each message takes eleven years to travel between the two planets. That means that Poobatron is eleven light-years away from Koozebane. Since it is stated that the Poobs are the Koozebanians' closest galactic neighbors, we can safely assume that Koozebane is the only inhabited world in its planetary system. Two planets that are eleven light-years away from each other can't be in the same system, the distance is too big.