You can tell a lot about a society by its movie demons, such as the fear of nuclear weapons parodied in “Dr. Strangelove” (1964, two years after the Cuban missile crisis) or the unease about biology run amok as captured in 1971’s “The Andromeda Strain”. In “The Day the Earth Stood Still”, which opens tomorrow nationwide, the great fear is environmental.

Because humans have so trashed Earth, a visitor from another planet—a benevolent-looking Klaatu, played by Keanu Reeves—arrives to eliminate humanity in order to save the planet. As he tells one earthling, “this planet is dying; the human race is killing it. . . . But if you die, the Earth survives.” Notably, in the 1951 sci-fi classic of the same name, Klaatu’s mission was to warn earthlings about the danger of nuclear weapons: “The threat of aggression by any group, anywhere, can no longer be tolerated,” he says at one point. “If you threaten to extend your violence, this Earth of yours will be reduced to a burned-out cinder. Your choice is simple: join us and live in peace, or pursue your present course and face obliteration.”

“The entire canon of science fiction in America in the Fifties was constructed in such a way as to reinforce Western fears of the Eastern Bloc,” producer Erwin Stoff says in the production notes. “The ‘other’ to be feared was always a metaphor for Communism. What was remarkable about [the 1951] ‘The Day the Earth Stood Still’ was that it placed the onus of responsibility on everyone equally. The ‘other’ to fear was ourselves—the nature of man and the terrible violence that humanity is capable of.”

The metaphors pile up fast and furious in the new version, too, and subtlety is not in abundant supply. But it’s a lot of fun—I won’t pretend to be a movie critic, so I won’t throw around any more adjectives. I'll just mention that you won’t envy astrobiologist the job Helen Benson (Jennifer Connelly) has of convincing Klaatu that mankind is worth saving.