If you discount numerous UFO and alien-abduction stories reported since the late 1940s-some fascinating, but all without a jot of proof-there isn't much reason to suggest that intelligent species exist beyond the Earth. On the other hand, the universe is vast; intelligent civilizations may be widely separated among the less common, Sun-like stars.
The idea of communicating with ETs began in earnest during the 1960s. Researcher Frank Drake, considered the father of SETI astronomy (SETI, short for Search for Extraterrestrial Intelligence), hosted the first SETI astronomy conference in the Appalachian Mountains of West Virginia in 1961.
Around the time of the SETI conference, Drake used the big 26-meter diameter radio telescope of the Green Bank, W.Va., observatory to study two Sunlike star systems: Epsilon Eridani and Tau Ceti.
I asked Dr. Drake about how he got the idea to use radio to eavesdrop on aliens.
Following a suggestion in 1959 by Cornell University physicists Giuseppe Cocconi and Philip Morrison, Drake said he proposed listening to two nearby stars at the 1,420 megahertz frequency (1 megahertz is one million cycles per second), the so-called magic frequency of the 21-cm line of neutral hydrogen. This location on the radio dial is now considered the universe's "waterhole"-the radio frequency at which intelligent species might consider a common place to talk and listen, much like the waterholes of Africa where animals come to drink (and humans came to hunt!).
Since hydrogen is the most abundant chemical element in the universe, Cocconi and Morrison reasoned aliens might transmit radio messages across the void in an effort to establish long-distance communication between the worlds.
Drake's ad hoc effort of listening for ET radio broadcasts was called Project Ozma.
"We named it after Frank Baum's Wizard of Oz's far away realm," Drake told me. "Needless to say, no alien broadcasts were ever detected over the months we listened to the deep sky."