ET is quiet. Searches for radio signals from other worlds have come up empty. And while the search continues, astronomers are thinking up ways to broaden the hunt. They’re looking for “signatures” of intelligent life other than radio transmissions. And they’re pondering just how many civilizations that are as “talkative” as our own might be out there.

One new study, for example, will hunt for two kinds of “technosignatures.” One of them is industrial pollution in a planet’s atmosphere. Molecules like CFCs — compounds that’ve damaged Earth’s ozone layer — don’t occur naturally. So if they show up in a planet’s atmosphere, they must have been put there by a civilization.

The other signature is the “glow” of massive arrays of solar cells on a planet’s surface or in the space around it. Researchers will identify which wavelengths they need to scan to see that glow.

Another study found that talkative civilizations probably are pretty rare. The study considered some features of stars that are key to life. And it assumed that other civilizations would develop in about the same length of time as our own.

The study said there should be about three dozen civilizations in the galaxy that are at the same stage of development as our own. They would be emitting radio waves, just as we do. But they’d be so far away that current technology might not be able to hear them. So we’d need new ways to discover these distant civilizations.

Script by Damond Benningfield

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