Does 'Planet 51' Really Exist?

The new animated film "Planet 51" (TriStar) boldly takes astronaut Capt. Chuck Baker where no one has gone before: to a life-harboring planet outside our solar system. There he finds a quaint 1950s society of little green people who are afraid of anything (or any one) that is different.

"In 1950s America, the drive-in was king and screen heroes fought invaders from outer space," said director Jorge Blanco. "But it was also a time of incredible social paranoia ? people actually believed that their neighbor could be an undercover agent trying to take over their minds."

"Shreck" screenwriter Joe Stillman unfolds the plot from there with thinly veiled spoofs of communist sympathizers, McCarthy-esque finger pointing, scientific ignorance and social change that will be lost on younger viewers but amusing to grown ups.

Chuck (voiced by Dwayne Johnson) lands his spaceship next door to a backyard barbeque in the "nice and peaceful" town of Glipforg, setting off a "War of the Worlds" panic that brings the military in from its top secret extraterrestrial tracking station known as "Base 9." Lem, the teenage junior assistant planetarium curator, and the one reasonable citizen on Planet 51, befriends Chuck and risks social ostracism and criminal charges to help the stranger from another planet.

Meanwhile, local hippies march in protest to the military action: "We're upset! We really are!"

Indeed, the world view on Planet 51 ? to say nothing of its cosmology ? is safe, predictable and narrow. The universe is 500 miles long and contains more than 1,000 stars. The only known intelligent life exists right there on Planet 51, where the comic-book store is "the greatest source of scientific knowledge."

In addition to clever messages about social tolerance, "Planet 51" gives us another chance to ponder the possibility of life on planets outside our solar system, as astronomers have done for nearly two centuries. As of last month, 405 so-called "exoplanets" orbiting far-away stars have been discovered in increasingly rapid fashion as new techniques allow scientists to zero in on and characterize the heavenly bodies. Thirty new exoplanets were discovered in October alone.

The red-dwarf star Gliese 581, located 20 light years from Earth, has at least four planets. One, called Gliese 581 d, is considered a "super-Earth" with a mass some 8 times that of our planet. To support life, scientists say a planet must orbit its star within a distance not too cold to freeze liquid water and not too hot to boil it. With a 66-day orbit around its medium-hot star, Gliese 581 d is squarely in the "just-right" zone.

This past August, Earthlings sent more than 25,000 messages to Gliese 581 d by radio telescope. Although close to Earth by astronomy standards, the planet is plenty far away; senders estimate the missives will arrive in time for the winter holidays in 2029.

But will Glieseans be advanced enough to respond?

Calculations by researchers at the University of Edinburgh suggest there could be at least 361 intelligent life forms in the Milky Way alone ? and possibly as many as 38,000 if you count life spreading from one planet to another during asteroid collisions. They looked at the combination of stars and planets needed to form a solar system that can support life, and the likelihood of life surviving long enough to develop into biologically complex and intelligent creatures able to communicate across the stars.

"Even if alien life forms do exist, we may not necessarily be able to make contact with them, and we have no idea what form they would take," said Duncan Forgan, a graduate student who carried out the research. "Life on other planets may be as varied as life on Earth and we cannot predict what intelligent life on other planets would look like or how they might behave."

Fortunately, on Planet 51 anyway, everyone learned how to get along.

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This article was provided to SPACE.com in partnership with the National Science Foundation.