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. Finding intelligent life in the cosmos is very optimistic for the near future.
Actually, scientist are looking for civilizations in outer space. The government have captured UFO’s and alien bodies, and is aware that they have been visiting Earth for centuries. Interestingly, the bodies of aliens appear that they could be androids, manufactured by an advance civilization. While being millions of years older than our society, they are living in a higher conscientious supported by these androids possibly. So, we know that they exist somewhere. We have never been alone in the cosmos. (OG,RTB)
*** Will Myers
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