There may be no greater unanswered question in the universe than the possibility of extraterrestrial life. Do aliens exist? Where are they? How many are there? Do extraterrestrial civilizations exist? There are no easy answers to those questions, but at least one astronomer tried to crack the code — and got the equation named after him.

Frank Drake, born in 1930, is one of the pioneers leading the charge in the search for extraterrestrial life. In 1960 he led an experiment, called Project Ozma, testing this original theory of electromagnetic emissions to search for intelligent life. (It was named Ozma after the fictional queen of the Land of Oz, as imagined by L. Frank Baum in The Wizard of Oz.) Drake and two other scientists spent 150 hours using a radio telescope to study two stars, Tau Ceti and Epsilon Eridani, 11 light years away (or 66 trillion miles). They received no sign or message of intelligent life, only static. But a year later, Drake convened with 12 other men (who later called themselves The Order of the Dolphin), to create the Drake Equation: a way to calculate the number of probable, communicating civilizations in the universe. Using this equation and multiplying a number of variables, they came up with anywhere from 10,000 extraterrestrial civilizations, up to one million.

So how does the Drake Equation work — and what have we learned about extraterrestrial life? Watch the video to see what Drake and astronomers after him have discovered about the possibility of aliens.