Life Beyond Earth at ScienceForKids.org

If aliens ever sent us a message, scientists hope to pick it up in a remote part of northern California.

There, in a clearing nestled amid the volcanoes of the Cascade Range, 42 radio dishes point together at the sky. The dishes, each 20 feet across, form a single, giant scientific instrument called the Allen Telescope Array. Scientists built the array to receive radio signals — the sort of message that could answer a very important question: Are we the only intelligent life in this vast universe?

“It’s a question humans have been asking forever,” observes astronomer Jill Tarter. Until recently, she directed the SETI (Search for Extra-Terrestrial Intelligence) Institute in Mountain View, Calif. “We read these ancient texts, and the ancient Greeks, the Romans, the Chinese — they were all wondering how we humans fit into the universe.” The SETI Institute helped build the Allen Telescope Array in hopes of finding some answers.

While the question is ancient, our understanding of the universe has changed over the centuries. We now know that stars do not hang from the sky like fruit on a tree. We also know Earth orbits the Sun and not the other way around. But we still don’t know if life exists elsewhere. And if extraterrestrial life does exist, does it have the technology to communicate with us on Earth?

If so, the Allen Telescope Array is listening, day and night, for some signal. From time to time, the dishes pivot toward a new patch of the sky. The array has not yet picked up any alien calls. So far, intelligent life appears limited to Earth.

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