That it rains rocks might explain why Glar does not have significant injuries after being savagely beaten by the police; aliens can take blunt force trauma as they're exposed to it regularly.
The Planet having a Ring might explain the reason why it rains rocks.
At a first glance, it'd seem that Planet 51 is extremely schitzophrenic. A 1950s culture, but a mastery of hovering already in place? Froglike humanoids alongside very familiarcanids? The belief amongst the aliens that the universe is "500 miles long"? It all doesn't add up. Then it hits: Planet 51? Planet #51? What if it's a Lost Colony?
The title is a double meaning. Chuck will know it as Planet 51 - it's probably thought by humanity to be an uninhabited planet. The planet's year is probably 1951 on top of that.
Fridge Horror: Just take a moment, let it set in that Chuck almost had his head sawed open.
The alien dog pees acid, right? he is going to be in Chuck's spaceship for a very long time, way longer than any dog can hold it. it will only be a matter of time before it leaks through to space, putting a hole in the ship.