Planet 51 answers a question sci-fi buffs have been asking for years. Filmdom tends to assume that alien visitors venture here to destroy us, but what if the roles were reversed? With our desire to conquer the cosmos, what if mankind stumbled upon a world where we got the E.T. treatment? Because the movie is tailored for children, Planet 51's target audience will pay these queries little mind and enjoy the zippy, colorful entertainment it serves up. But beneath its Everestian mountain of pop culture references is a flick adults can admire just as much, especially if they're students of UFO cinema.

In a galaxy not so far away, there exists a planet stranded in the '50s. While we earthlings move forward in time, little green men still listen to doo-wop and flock to sci-fi schlock about human invaders. But what's fantasy to them becomes reality when astronaut Chuck Baker (voice of Dwayne Johnson) touches down in their suburbia. The intrepid explorer flips out upon his close encounter, though he finds a friend in Lem (voice of Justin Long), an alien teen who sees him more as a preening wuss than a looming threat. But try telling that to General Grawl (voice of Gary Oldman), who considers Chuck a menace and whips the whole planet into a frenzy as he sets out to blow him to kingdom come.

The past few months have seen family films get too cerebral (Where the Wild Things Are) and too noisy (Astro Boy). Perched between the two looms Planet 51, whose script won't win any awards yet isn't total junk food. Its intent appears the same as Monsters vs. Aliens, although this one actually makes good on its promises. While the latter passed on paying homage to the monster movies of yore, Planet 51 is fully aware of where its roots are. This means sifting through a lot of tiresome reference gags, though the movie does well in wrapping it all up in a story inspired by the heyday of science fiction. Planet 51 is as inspired by '50s B-movies as by the era's political climate, creating a Cold War allegory you don't need Edward R. Murrow to appreciate. There's the odd bit of humor catering to adults, but nothing here will leave the little ones scratching their heads.

A vibrant style emerges as another of Planet 51's strong suits. Obviously not as polished as what the Pixar crew can do in their sleep, this movie is lively and even eye-popping on occasion. The aliens' cozy hometown isn't far off from our nostalgic recollections of the '50s, and character design comes across as quite competent. There's even a little robotic rover (sort of a sleeker WALL-E) who pitches in a bit of fun comic relief. The voice acting is good, although it's evident the filmmakers went for familiar names over suitable tones. Johnson fits the bill as lunkhead Chuck, and Long nails hormonally-challenged Lem to a tee. But Jessica Biel is completely dispensable as Lem's love interest (you can't even tell it's her, and not in a good way), and Oldman's Grawl is a ho-hum antagonist. The story also goes through its share of padding and arbitrary humor, although the ultimate lesson about not being afraid to discover the unknown seems pretty sound.

Although Planet 51 doesn't have the pedigree of an Up or the ambition of a Fantastic Mr. Fox to make a great dent in the world of animation, it was made to show viewers a good time, and without their brain cells becoming collateral damage. Planet 51 isn't out of this world, but it's perfectly pleasant fare for all budding Buzz Lightyears.

MY RATING: *** (out of ****)

(Released by TriStar Pictures and rated "PG" for mild sci-fi action and some suggestive humor.)