"General, I know what you're afraid of, and it's not Chuck. It's not monsters or aliens. It's the unknown. I've spent my whole life running from it, and I think maybe you have too, but I'm telling you the unknown isn't something to be afraid of. It can be your best friend. And just when you think that it means the end of everything you know, it's really just the beginning."
— Lem, to General Grawl
Planet 51, a Spanish/American All CGI Cartoon feature from 2009, is an Affectionate Parody of tropes from both Science Fiction and Sit Coms of The Fifties.The premise: Human astronaut Captain Charles "Chuck" Baker, accompanied by an exploration robot named Rover, lands on the eponymous planet, which is supposedly uninhabited. However, Planet 51 is populated, by green-skinned humanoids whose world strongly resembles 1950s suburban America. The aliens are also paranoid about being invaded by another planet, so Chuck's appearance causes unintentional havoc, and he's soon being hunted by the military. Chuck befriends an alien teenager named Lem, a worker at a local observatory; Lem protects the astronaut as he struggles to return to his ship, which will automatically take off after a preset time limit whether Chuck is aboard or not.
Artistic License - Astronomy: An In-Universe example. According to Lem's observatory lecture at the beginning of the film, "the universe is nearly 500 miles long, and it contains—you're not going to believe this—over 1000 stars!"
This is apparently a running thing with the aliens' unit measurements - they seem to just use lower numbers for things in general: at one point the professor postulates that a manned space flight would cost "hundreds of dollars."
Possibly Fridge Brilliance: he mentions at some point that the only thing he does with the star ship is to push some buttons, like a monkey could do. Chuck isn't exactly the brightest bulb of the set...
Tertiary Sexual Characteristics: The female aliens have built-in, organic "high heels" on their feet. Word Of God (aka character designer Ignacio Güejes, in the book The Art of Planet 51) explains that this is because "we discovered that if the females had that extra heel on their feet, they would move differently than the male aliens, with swaying hips."
Cannot Spit It Out: Lem has a hard time asking Neera out on a date. This is partially due to his own shyness, and partially because Glar is a Moment Killer who bursts into song whenever Lem is about to ask Neera out. Technically, Lem never completes his question to Neera, because at the end of the film she says "yes" before he can finish.
City of Adventure: Glipforg, the quiet little suburb where Chuck lands.
Cloud Cuckoolander: Skiff, a sci-fi nerd who takes aliens a little too seriously, even before one of them arrives.
Expy: The Aliens' pets look like Xenomorphs that are about the size of a toy poodle. They have a sucker mouth on a frog-tongue, instead of a second set of jaws, though.
The Fifties: Parodied by the culture of the aliens.
Hassle Free Hotwire: Chuck and Lem both do this. Lem lampshades it by explaining to Neera that hotwiring is "how they start cars on Earth."
Heel Face Turn: General Grawl does one after Chuck saves his life.
Hidden in Plain Sight/Status Quo Is God: How do you hide an alien astronaut? Paint an eyeball on his space suit and enter him in a costume contest promoting the Alien Invasion movie that just happens to be premiering today. Double for Status Quo because even though the "invasion" has the military in a tizzy, the movie premiere isn't even delayed!
Hoist by His Own Petard: Professor Kipple extracts the brains of the soldiers that have been tricked by Chuck into believing they have been brainwashed. At the end of the film, the two soldiers practice the same operation on the Professor.
Product Placement: At one point Chuck pulls a Twix bar out to convince Lem to clear the way to his ship. It's not quite clear how he got that into space with him.
Rule of Funny: How likely is it that an alien civilization that has had little contact with Earth, which hasn't been revealed to the public, would evolve into a near-perfect duplicate of a specific human culture? And how likely is it that such a world would have a popular science fiction franchise called Humaniacs? Who cares?
Scenery Porn: The film's backgrounds are just breathtaking.
Sitcom Arch Nemesis: Lem seems to see Glar as an antagonistic competitor, only because Neera seems interested in him; in actuality, Glar's been on his side the whole time.
Soundtrack Dissonance: The advertisement for the film uses The Killers' "Spaceman." The song is about being abducted by aliens and then being autopsied.
Stealth Pun: Chuck's MP3 player has a picture of a pot as its logo, making it, presumably, an iPot.