The nearest planet that is similar in size to Earth and located within the narrow habitable zone of its star is unromantically named Kepler-186f. If there is life on this planet, none of us will ever know. That's because Kepler-186f is 493 light-years away [source: Vergano].
When the search for extraterrestrial intelligence (SETI) began in the 1960s, astronomers quickly dismissed the idea of physically visiting an alien planet. The technological advances necessary to shoot humans across the galaxy is, like the nearest habitable planet, still light-years away.
Instead, the SETI sciences decided to stay on Earth, but keep an ear on the heavens. If intelligent life is out there, SETI decided, then it must have an understanding of radio waves and the electromagnetic spectrum. Like us, the alien species probably doesn't have unlimited energy resources to travel around the universe looking for friends. The most efficient way to say, "Hello, universe. We're here!" is to send a radio transmission.
The next question for SETI scientists was where to listen? The best guess was promoted by two Cornell physicists in the early 1960s, Philip Morrison and Guiseppi Cocconi. The two men assumed that an extraterrestrial life-form intelligent enough to master the electromagnetic spectrum would try to craft its message in a "common language" that anyone could understand [source: Kiger].
The most common electromagnetic frequency, Morrison and Cocconi reasoned, is emitted by the most common element in the universe, hydrogen. If an alien was trying to communicate with us over an open channel, it would choose 1420 megahertz, also known as the "hydrogen line."
And so began the search for alien life. Using large radio telescopes, astronomers focus on one tiny patch of sky and listen for the faintest sign of an unusual transmission coming over the 1420 MHz frequency. After listening for a few minutes, the telescope moves on to the next tiny patch of sky, and so on, and so on [source: Andersen].
And that's exactly what Jerry Ehman and other SETI volunteers were doing with the Big Ear telescope at Ohio State back in the summer of 1977. They were listening to a sliver of the sky near the constellation Sagittarius and measuring the strength of the signal picked up on the 1420 MHz channel.
Ehman and others had been at it for years, always receiving the same 1s and 2s of normal background radiation, until Aug. 15, when the Big Ear picked up a startling signal that would echo through the decades.
Next we'll find out why the "Wow!" signal makes such a great case for being a message from ET.