One of them is Lem (voice of JUSTIN LONG), a teenager who's just been named assistant curator at the local planetarium, a promotion he hopes might impress his next door neighbor, Neera (voice of JESSICA BIEL). He has a crush on her -- something not missed by her younger brother, Eckle (voice of FREDDIE BENEDICT) -- but doesn't know how to proceed. That's unlike his more carefree friend, Skiff (voice of SEAN WILLIAM SCOTT), who works at the local comic book store, or hippie Glar (voice of ALAN MARRIOTT) whose social protesting has grabbed Neera's interest.

But Lem has bigger fish to fry when he ends up being Capt. Baker's unintentional and initially unwilling accomplice to harbor the astronaut and get him back to his spaceship. That goal quickly becomes complicated upon the arrival of the army, led by General Grawl (voice of GARY OLDMAN) who wants the alien captured. He gets his advice from Professor Kipple (voice of JOHN CLEESE) who spreads rumors about such invaders, such as them turning the locals into zombies, his paranoia no doubt fueled by such related films.

From that point on, Lem does what he can to help Capt. Baker as they and their friends try to avoid Grawl, his men, and Kipple who wants the astronaut's brain for testing.

Yet, if such travel somehow became possible -- say through a discovered or created wormhole, would we be peaceful and just want to establish contact, or simply follow our species' long-running, historical tradition of conquering others and taking their land, culture and such for their own?

More interestingly, what would inhabitants of other planets think of our visit and would they have any prior knowledge of us, such as from our old TV broadcasts racing across the cosmos and making them think -- due to the amount of time it would take such transmissions to reach them -- that 1950s America is who and what we are?

There's no direct evidence that such incidental wavelength contact created the culture found in "Planet 51," but the filmmakers have certainly made sure we don't miss the cultural and temporal setting of this lively but not terribly engaging animated comedy. They've also thrown in about every sci-fi film reference know to man or alien in this offering that works far better in the small details than in the overall picture.

Working from the screenplay by Joe Stillman, our three (yes, count 'em, three!) directors -- Jorge Blanco, Javier Abad and Marcos Martinez -- set up this foreign civilization straight out of "Happy Days," "Back to the Future" and any number of other sanitized fictional versions of the '50s (albeit with a wide array of futuristic, sci-fi touches), complete with UFO paranoia and related movies about alien invasion.

The twist, of course, is that humans -- named humaniacs here -- are the space invaders in their films. Then, faster than one can say "fact is stranger than fiction," such an alien touches down on their planet in the form of square-jawed but lily-livered Captain Charles T. Baker.

The civilized, green-skinned and four-fingered inhabitants freak out, as does the human due to his unexpected discovery of them. The military then rolls in, and comedic chaos ensues as the astronaut tries to get back to his ship to get out of Dodge, all while nearly ruining the life of a local teen who unintentionally becomes his ally.

This is the second computer-animated film of 2009 to feature English-speaking humans as the invaders of other worlds (the first being "Battle for Terra"), and it's hard to tell if that's just coincidence (although Hollywood has a long track record of releasing similar movies within months of each other) and/or if it's some sort of thematic message regarding America's military involvement in other lands.

While the prior flick could certainly be seen that way, such a message -- if at all intentional -- certainly takes a back seat to the comedy and satire here, designed to appeal to viewers of all ages. Methinks the younger the viewer, the more likely they'll enjoy what's offered, although there are enough amusing small touches (especially for movie buffs counting all of the cinematic references or those who like some wink-wink, nudge-nudge naughtiness thrown into a kids movie) that adults won't find this a chore to sit through.

It's just too bad that the same degree of attention to minute and brief details wasn't applied to the overall story and characters. What's there is serviceable, but never transcends its rote nature to become something special, magical or emotionally engaging.

While watching this play out, I couldn't help but think what the likes of Pixar could and would have done with the material to give it that special quality. The technical work is fine, even if photorealism is clearly never the goal of the retro visuals, while the vocal work from the likes of Dwayne Johnson, Justin Long, Jessica Biel, Gary Oldman and others delivers what's required.

Entertaining enough to watch as it unfolds but not much more, "Planet 51" is an okay diversion, but really isn't the best example of an Earth-made, computer-animated comedy for some alien civilization to pick up while scouring the heavens for sign of intelligent life somewhere else in their universe. It rates as a 4 out of 10.