Are You There, E.T.? SETI Finds No Alien Signals from Exoplanets

February 9, 2013 - Intelligent alien life is likely relatively rare throughout our Milky Way galaxy, with fewer than one in a million solar systems harboring civilizations advanced enough to send out radio signals, a new study reports.

A research team that includes famed alien hunter Jill Tarter — the model for astronomer Ellie Arroway in Carl Sagan's famous book "Contact" — surveyed dozens of planet-hosting stars for radio signals from alien civilizations. They turned up nothing.


"No signals of extraterrestrial origin were found," the researchers conclude in the study, which has been accepted for publication in The Astrophysical Journal.

The team selected 86 stars using data from NASA's planet-hunting Kepler space telescope, and also observed 19 stars that serendipitously fell within range as they searched the primary targets. (One planet candidate turned out to be a false positive, reducing the total number of targets to 104.) [Gallery: A World of Kepler Planets]

The researchers were working with the catalog of Kepler planetary candidates, which at the time included 1,235 possible exoplanets. (That number is now up to 2,740, with 105 of them confirmed to date.)

In the next stage of research, alien hunters plan to listen in on communications between two exoplanets.

The astronomers limited their search to stars that host five or six planet candidates, some of which reside within the habitable zone — the range of distances from a star where liquid water can exist on a world's surface. The selected stars are about 1,000 light-years to 1,500 light-years from Earth.

Radio signals in narrow, focused bands are a possible indication of intelligent life, given that humans generate such signals here on Earth.

So, using the Robert C. Byrd Green Bank Telescope in West Virginia, the team probed each star system for five minutes between February and April 2011. They examined the planets in a radio-frequency range of 1.1 to 1.9 GHz, which is between the cell phone and television bands used on Earth.

This range of frequencies includes a so-called "watering hole" between 1.4 GHz and 1.7 GHz, where hydrogen and hydroxyl (both components of water) emit signals from quantum processes detectable in radio telescopes.