In Hollywood, extraterrestrials always seem to favor the grand entrance. They land on the White House lawn and implore us to end our violent ways (The Day the Earth Stood Still, 1951). They replace the citizens of a California town with listless pod people (Invasion of the Body Snatchers, 1956). They persuade Richard Dreyfuss to play with his mashed potatoes (Close Encounters, 1977). They even look like David Bowie (The Man Who Fell to Earth, 1976). Right now, in fact, two unrelated alien posses are invading theaters near you: the insectoid stars of District 9, who make their presence known by parking a UFO above Johannesburg, and the hyperactive green gremlins of Aliens in the Attic, who battle a group of plucky tweens over a Midwestern rental home. (Listen to Andrew Romano on our fascination with whether aliens exist.)
But even if E.T. exists off the silver screen, the chances that he'll discover us any time soon are vanishingly slim (Reese's Pieces or not). After all, projects like SETI (Search for Extraterrestrial Intelligence) have been waiting since 1960 for aliens to make contact—without hearing the slightest peep. The good news, however, is that some scientists are finally focusing on the other side of the equation: a series of high-tech missions designed to help us find them. And even at this early stage, the circumstantial evidence they've gathered has made it clear that we're probably not alone in the universe.
Here's what we know. In 1995, Swiss astronomers pinpointed the first-extrasolar planet. Unfortunately, it was a giant ball of gas orbiting so close to its sun that it glowed with enough heat and radiation to vaporize even the hardiest little green men. But at least the discovery proved that planets occurred outside our own cozy solar system. A few years later, "super-Earths" started to reveal themselves—smaller, firmer, at a discrete distance from their companion stars. Although these planets are much larger and less temperate than ours, they prompted some astronomers to estimate that perhaps half of the 200 billion or so suns in the Milky Way support terrestrial, Earth-like worlds.
We've also discovered that water, the essential ingredient for life, exists elsewhere in the universe—starting with our own solar backyard. Robots have spotted gullies freshly carved in the sides of Martian hills—evidence of recent upwellings. In June, astronomers observed geysers of water vapor on Enceladus, one of Saturn's moons. Even ghastly Jupiter is a candidate—or at least its moons Ganymede, Callisto, and Europa, the last of which may have oceans larger than ours hidden beneath its crust of perpetual ice.
The question now is how many of those 100 billion potential Earths can we reasonably expect to have harbored H2O and served as a cradle of life, intelligent or not? Enter Kepler, an ambitious new NASA mission. Launched via satellite in March, Kepler's $600 million space telescope uses a sophisticated photometer to stare at all 100,000 stars located in a particularly promising region of the Milky Way while measuring the size and orbit of every planet that passes in front of them. The larger the shadow, the larger the planet; the more often it appears, the closer the orbit. The point is to isolate for the very first time alien worlds orbiting alien suns at distances where temperatures are right for liquid water and possible life. "This mission is like Columbus," says principal investigator Bill Borucki. "We will get Earth-sized planets, terrestrial planets, in the habitable zone. It won't be 'close.' We will know."
The concept behind Kepler isn't new. Borucki—the sort of guy who skipped high-school projects to build elaborate UFO transmitters—constructed his first photometer in college; he started thinking about how to apply the technology to the search for extraterrestrial life shortly after arriving at NASA in 1962. It wasn't until the early 1980s, however, that Borucki began publishing papers on photometry and pushing his bosses to finance a photometric mission. Their response? It's impossible. Undeterred, his team slaved over the project for the next two decades, inventing new technologies, showing they could achieve the necessary precision, and applying for additional funding at every turn, until finally, in 2001, NASA "said uncle," as Borucki puts it. After only 10 days in orbit, the satellite measured a dip in starlight of a few parts per million caused by a distant Jupiter, proving that it's sensitive enough to detect Earth-like planets. By 2013, says Borucki, Kepler is likely to have located "hundreds or even thousands" of potentially habitable worlds.
Where we'll go from there is still unclear. But assuming that people are as fascinated by the discovery of real-life Earths as they are by, say, Will Smith fighting off alien invaders, we might launch a telescope designed to scan auspicious planets for the presence of CO2 and ozone, then invent a more intricate device to suss out whether these atmospheres contain isotopes of oxygen consistent with living systems. The final step, says Borucki, is "a probe that can travel near the speed of light and gets there, shows us pictures, listens to their radio stations and television stations, and gives us a much better understanding of this new planet."
We're not at the Star Trek stage yet. But given enough time and interest—and enough money—scientists believe the possibilities are limitless. "I've suggested nothing that we don't know pretty much how to do currently," Borucki says. "After Kepler, I cannot imagine people saying, 'I don't care about life. I don't care about these wonderful civilizations that might exist.' " So let the search continue—assuming, of course, that E.T. doesn't show up at the White House first.