Released yesterday on DVD: "Planet 51"

Grade: C

The agreeable but flagrantly unoriginal Planet 51 belongs to the mix-and-match school of animated moviemaking that operates on the plaintive hope that familiarity is the surest path to the box office. Almost every element of the film, created by Ilion Animation Studios, based in Madrid, is borrowed from earlier films, then tweaked (and invariably softened) to become a reference rather than a copy.

Directed by Jorge Blanco, from a story by Joe Stillman, it portrays the inhabitants of Planet 51 in a faraway galaxy as smaller, green, Shrek-like creatures with antennas, webbed feet and squished noses. They go into a tizzy when a flag-toting American astronaut, Charles, or Chuck, Baker (voiced by Dwayne Johnson, a.k.a. the Rock), sets down on their territory. At his side is an intrepid, seemingly indestructible, rock-collecting little robot (R2-D2 meets Wall-E) of doglike loyalty named Rover, minus the personality quirks of its forerunners.

When Chuck arrives, Lem (Justin Long), a 16-year-old sci-fi dweeb and a budding astronomer who works at a mountain observatory, becomes his protector and (in shades of E.T.), hides the astronaut in his suburban bedroom. Lem has a crush on his independent-minded neighbor Neera (Jessica Biel), a teenage Miss Piggy with plump lips who is there strictly to give the movie a dollop of tepid romance.

Other references include a lamppost dance to the tune of Singin’ in the Rain, a blast of Also Sprach Zarathustra (from 2001: A Space Odyssey) and a comic routine by Chuck that quotes from half a dozen sci-fi classics.

A central joke of the movie is that Planet 51 is a comic-book version of 1950s America, with its popular songs (Long Tall Sally and Lollipop are heard), its taste in science fiction and its flying-saucer paranoia.

It is of no comfort to the planet’s fearful populace that Chuck is a vain, dim-witted, aw-shucks ladies’ man, who happens to speak the same language (English), despite coming from 20 billion miles away. (The movie doesn’t bother to make anything of the coincidence.) Chuck barely knows how to operate a spacecraft, having coasted the distance on autopilot.

When the inhabitants are told that he is an evil alien, wielding mind control that will turn them into zombies, they believe it. Leading the charge against Chuck and Rover are General Grawl (Gary Oldman) and his ally Professor Kipple (John Cleese), a mad scientist spouting outlandish nonsense who is intent on extracting the astronaut’s brain for research.

Early on, the movie turns into a protracted game of hide-and-seek in which the big bad army (portrayed as a bunch of gun-crazy incompetents mugging ferocity) pursues and captures Chuck and keeps him in a subterranean military base. It remains for Lem and his pal Skiff (Seann William Scott), among a handful who recognize that Chuck is friendly, to help him escape and return to Earth, and for Chuck to become serious about taking command.

Although Planet 51 aspires to the same tone as the Shrek movies (Stillman was one of several screenwriters on the first two Shrek films), the dialogue lacks the facetious bite of its antecedents, in which the wisecracks never stop while gently pushing the envelop. The timidity of Planet 51, which doesn’t even make the pretense of subversion, owes partly to its being pitched to a younger audience and partly to its creators’ paucity of wit. Many opportunities for sharper satire are squandered, and what mild humor there is peters out in a final burst of triumphal ickiness.