Radio silence from TRAPPIST-1’s seven Earth-sized rocky planets

Alien hunters have already begun checking out a newly discovered planetary system for any messages from ET. And the news so far is that if intelligent life exists on any of the seven Earth-sized rocky planets, it is keeping itself to itself.

View from TRAPPIST-1f
This artist’s concept is one interpretation of what it could look like from the surface of rocky planet TRAPPIST-1f. Image credit: NASA/JPL-Caltech

Astronomers from the SETI Institute – it stands for Search for Extra-Terrestrial Intelligence – turned a collection of radio telescopes onto red dwarf star TRAPPIST-1. This ultra cool star, just a little bigger than Jupiter, lies just 39 light-years away, which is right on our cosmic doorstep, and has at least three rocky worlds warm enough to host life.

The alien hunters pointed the 42 dishes forming the Allen Telescope Array in California at the star last year when three of the seven planets had already been detected. For two days, they scoured the region around TRAPPIST-1, scanning through ten billion radio channels to listen for any signals from ET. No transmissions were detected.

Seth Shostak, Senior Astronomer at the SETI Institute, said on the organisation’s blog: “How sensitive was this search? Assuming that the putative inhabitants of this solar system can use a transmitting antenna as large as the 500-metre FAST radio telescope in China to beam their messages our way, then the Allen Array could have found a signal if the aliens use a transmitter with 100 kilowatts of power or more. This is only about ten times as energetic as the radar down at your local airport.”

Other scientists point out that life in the TRAPPIST-1 star system might only have advanced to the level of microbes or simple organisms.

Allen Telescope Array
Part of the Allen Telescope Array, built by the University of California at Berkeley, near San Francisco, which is used to listen for possible signals from E.T. Image credit: Colby Gutierrez-Kraybill via Wikimedia Commons.

The alien hunters are planning to make further attempts to tune in to the planets using their radio telescopes. And a new NASA observatory being launched next year, the James Webb Space Telescope, will be powerful enough to detect any chemical signatures in the planets’ atmospheres that would indicate life.

Dr Amaury Triaud, of the Institute of Astronomy, Cambridge, who was part of the discovery team, told Skymania: “From the cocktail of molecules detected, we will deduce whether there is active biology on the surface or whether the planets are barren.

“I prefer using the term “biology” because if I say life, people imagine little green men. Here we are looking at bacteria, plants – the sort of more inert type of life.”

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By Paul Sutherland

Paul Sutherland has been a professional journalist for nearly 40 years. He writes regularly for science magazines including BBC Sky at Night magazine, BBC Focus, Astronomy Now and Popular Astronomy, plus he has authored three books on astronomy and contributed to others.

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