The Grebulons are a sapient species. A colony of Grebulons is located on a trans-Neptunian planetary body nicknamed Rupert; they are monitoring Earth television and radio broadcasts, but do not know why.
As it turned out, the spaceship which was carrying the dormant Grebulons with their minds and memories stored for some reason within the spaceship's computer; was unfortunately hit by an asteroid at the precise point containing the apparatus built to detect and warn its systems in case of the ship getting hit by an asteroid. Said computer files were destroyed during the collision, and thanks to the confusion of the ship's computers and robots, so were the backups. After the confused Grebulons awakened, they managed to recover only the slightest bits of information about their mission; which told them to "land" somewhere and "monitor" something. With limited options available, they landed on the first planet they found and started monitoring the first thing of interest they detected; which happened to be Earth's transmissions.
Behind the scenes
- The Grebulons are featured in the Douglas Adams book Mostly Harmless.