The Kepler space telescope opened a new era in the search for exoplanets finding more than 4,000 candidates of which nearly a thousand candidates have been confirmed. The SETI (Search for Extraterrestrial Intelligence) project has recently studied 86 planets found by 2011 to search for radio signals that could indicate the potential presence of an alien civilization.
SETI’s research was performed using the Green Bank Telescope, part of the National Radio Astronomy Observatory (NRAO) in West Virginia. It’s the largest steerable radio telescope and with its 100 m in diameter combines versatility and sensitivity.
The 86 planets have been chosen for their characteristics. The surface temperature is estimated at between -50 and 100 degrees Celsius (-58 to 212 degrees Fahrenheit), a radius under three times that of Earth and an orbital period greater than 50 days. Those are conditions that put these planets in the habitable zone around their star, where there may be liquid water on at least part of the surface and where life forms of the kind as we know could emerge.
SETI’s research has covered a wide range of radio frequencies. The idea was to try to pick up possible radio signals with the express purpose of communicating with alien civilizations and at the same time possible signals similar to those of radio and TV broadcasting.
Among these frequencies those belonging to the so-called terrestrial microwave window are included. They can travel through interstellar space and the Earth’s atmosphere with little distortion. A part of these frequencies is linked to hydrogen and hydroxyl molecules. For these reasons, an intelligent civilization might choose them for sending interstellar messages.
No radio signal was picked up from the 86 planets studied. This means that almost certainly none of them is inhabited by sentient creatures that use radio waves to communicate. In theory, those planets might be inhabited by non sentient life forms or there could be sentient creatures who use media other than radio waves to communicate.
One of the most difficult things to imagine for SETI and for anyone who wonders about possible alien civilizations is getting into a mindset that is by definition alien. The issue is even more difficult when one tries to understand how a civilization more advanced than the human one could communicate, considering that it could use inventions and discoveries that are unpredictable for us. It’s a really complex problem but very intriguing.
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