Reasons to Believe

A Targeted Search for Extraterrestrial Intelligence Found Nothing, Part 1

The goal of NASA’s Kepler satellite mission is to find planets that could host extraterrestrial life and possibly even intelligent life. Hundreds of “Kepler objects” have been detected so far. A research team attempted to detect signals from selected Kepler objects that might indicate an intelligent source, but no such signs were found. This two-part article series explains why a null result should not be surprising and why, if naturalism is true, additional searches have a negligible chance of success.

Jay Hanna “Dizzy” Dean, the most successful pitcher of his era, led the St. Louis Cardinals to victory in the 1934 World Series. In the fourth game, as Dizzy was sliding into second base to avoid a double play, the ball hit him in the head and knocked him out. Upon being released from the hospital, he told the press, “The doctors x-rayed my head and found nothing.”

Like Dizzy’s doctors, astronomers searching for extraterrestrial intelligence (ETI) have found nothing.1 Last year, members of the Search for Extraterrestrial Intelligence (SETI) Institute (including Jill Tarter, the holder of the Bernard M. Oliver Chair for SETI and the inspiration for Jodi Foster’s performance in the movie Contact), members of SETI at Berkeley, and several radio astronomers teamed together in an attempt to detect signals of intelligent life. The group searched 104 stars, hosting a total of 164 exoplanets that had been detected by NASA’s Kepler satellite, without success.

Their work exposed the difficulties in detecting other technically advanced civilizations in the Milky Way Galaxy (MWG). Part 1 of this series will look at the parameters and methodology of the search. Part 2 will present technological and scientific reasons for the null result of the SETI project, as well as reasons why there is little hope (given materialistic naturalism) of finding galactic neighbors who have technological civilizations.

Targeted Searches Only Recently Possible

Past searches for ETI have consisted of star surveys using instruments like the Allen Telescope Array and other radio telescopes. With the discovery of almost 1,000 exoplanets, things have begun to change. Now, searches can target specified exoplanets and the 2009 launch of the Kepler satellite has been the biggest boon to enabling these targeted investigations. Prior to Kepler, exoplanet detection technology tended to favor gas giant planets. Thus, it is no surprise that most of the first exoplanets discovered are not suitable hosts for any life, much less sentient beings. However, the transit method used by Kepler is designed to detect Earth-size planets that are in or near the habitable zone of their host star. A recent update of NASA’s Exoplanet Archive listed another 119 Kepler-discovered planets around 59 stars; many are in multiple planet systems. In addition, there are stars termed “Kepler Objects of Interest” (KOI) from which there are over 3,000 detections that have not yet been verified as planets.2 These exoplanet “candidates” are also available as possible targets for SETI searches.

Selected Targets Most Amenable for Earth-like Life

Eighty-six Kepler-observed stars (those having confirmed exoplanets and KOIs with detections still classified as candidates) were selected as targets for the SETI survey. These stars were selected because they satisfied one or more of the following criteria:

  • Star and planetary system have a cursory similarity to Earth and the solar system
  • Star hosted one or more planet candidates that were in or near the traditional habitable zone3
  • Star hosted five or more planet candidates total
  • Star hosted a “super-Earth”4 in an orbit with a period of more than 50 days

The SETI project later found that one of the 86 targets is a false positive; so it was deleted from the list. However, 19 other KOIs were serendipitously located close enough to the beam width of a primary target such that these stars were also observed, giving a total of 104 possible planetary systems under observation for evidence of ETI.

The Unique Earth-based View of Kepler Objects

The SETI team’s strategy was to look for narrow band (<5 Hz) radio emissions from a civilization communicating with other planets in its home system. In the case of human civilization, this would be analogous to radio transmissions to/from spacecraft or occupied stations in orbit around or on the surface of our sister planets. Additionally, Earth-based radar imaging of solar system bodies and radar mapping of debris from artificial Earth satellites would produce narrow band radio frequency transmissions of interest. Similar activities would be expected of extraterrestrial civilizations. Transmissions of this type would be directed in the plane of the planet’s orbit around its host star.5

The Kepler satellite’s transit detection method works best when a planet’s orbit is seen nearly edge-on from Earth’s vicinity. Thus, the Kepler objects were ideal for this ETI search strategy. Each of the exoplanets in a system observed by Kepler orbited their host star in nearly the same plane, with Earth currently passing approximately through that plane. So it should be possible, in principle, for an Earth-based receiver to intercept any narrow band communications between exoplanets in one of those systems.

The research team explained why narrow band radio emissions would be a good indicator of ETI:

Radio emission less than 5 Hz in spectral extent is currently known to only arise from artificial sources...Natural astrophysical electromagnetic emissions are inherently spectrally broadened by the random processes underlying natural emission physics...Emission no more than a few Hz in spectral width is, as far as we know, an unmistakable indicator of engineering by an intelligent civilization.6

Yet in spite of the leaps in our technology and knowledge of exoplanets, these research efforts have not detected any signs of intelligent life. Part 2 will explore why this null result is not surprising.

Dr. Otis F. Graf Jr

Dr. Otis Graf received his PhD in aerospace engineering from the University of Texas at Austin in 1973. He worked at the NASA Johnson Space Center and for IBM Government Systems. Since retiring from IBM, he has served as an online instructor for Reasons Institute and is living in Katy, TX.

Subjects: SETI

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  1. Andrew P.V. Siemion et al., “A 1.1 to 1.9 GHz SETI Survey of the Kepler Field: I. A Search for Narrow-band Emission from Select Targets,” preprint, arXiv:1302.0845,
  2. The transit methodology requires that multiple transits of a planet across the face of the star must be observed before the object is confirmed as an exoplanet. That means it could take many months, even years, after the initial detection for astronomers to make a confirmation.
  3. A planet in the traditional habitable zone has an equilibrium surface temperature that would allow liquid water on the planet’s surface.
  4. A super-Earth is defined as an exoplanet with a radius that is less than three Earth radii.
  5. Planetary formation and evolution models generally predict that planets in a system will be found in orbits that are nearly coplanar. However, gravitational interactions between the planets could move planets into inclined orbits.
  6. Siemion et al., “A 1.1 to 1.9 GHz SETI Survey of the Kepler Field.”