1960

SETI

Giuseppe Cocconi (1914–2008), Philip Morrison (1915–2005), Frank Drake (b. 1930)

Are we alone—in the solar system, the galaxy, or the universe? People have asked that question throughout (and before) recorded history, but only in the last century or so have we started to develop the means to find out. The 1931 discovery of natural sources of extraterrestrial radio waves (from the galactic center, and, later, from Neutron Stars and other high-energy objects) provided a route to address the question, because it became clear to astronomers that radio signals could travel vast distances across interstellar and intergalactic space.

The concept of radio communication across vast galactic distances became a serious topic of scientific study in 1959, when the physicists Giuseppe Cocconi and Philip Morrison published a paper in Nature entitled “Searching for Interstellar Communications.” In that work they described ways that astronomers might search for radio signals transmitted by other civilizations. The challenge was almost immediately taken up by the radio astronomer Frank Drake, who in 1960 used the 85-foot (26-meter) radio telescope at the National Radio Astronomy Observatory in Green Bank, West Virginia, to conduct the first dedicated search for nonnatural radio transmissions from nearby, Sun-like stars. Drake’s search was not successful, but it spurred what has now been a more than 50-year international observing campaign called the Search for Extraterrestrial Intelligence (SETI). Drake also developed a crude estimate of the potential number of civilizations in our galaxy (N_C): number of stars (N_*) × fraction with planets (f_P) × number of habitable planets (n_HZ) × fraction with life (f_L) × fraction with intelligent life (f_I) × fraction with technological civilizations (f_C) × the lifetime of those civilizations (L). Known as the Drake equation, this yields estimates ranging from 1 (Earth) to potentially millions of intelligent civilizations in the Milky Way.

Given recent discoveries of extremophile life forms on Earth and of habitable extrasolar planets around other nearby stars, many SETI participants (now including the general public, thanks to the Internet) remain optimistic about the long-term potential to make contact. Of course, if we don’t listen, we may never know. . . .

This Hubble Space Telescope view of star formation within giant molecular clouds in the Eagle Nebula forms a fitting backdrop for the famous Drake equation.