Astronomers have discovered a nearby Earth-sized planet in the direction from which mysterious radio signals were heard earlier this year.
The planet, dubbed Ross 128 b, lies only 11 light-years away, which is right on our cosmic doorstep, and could be habitable because it enjoys moderate temperatures.
Its discovery will excite alien-hunters wondering whether unexpected radio emissions picked up by a giant telescope in Puerto Rico in May could be a message from E.T.
The Planetary Habitability Laboratory detected the broadcast using the Arecibo radio dish in Puerto Rico to study a red dwarf star, Ross 128, as part of a search for Earth-like planets.
Professor Abel Méndez reported afterwards that the team had recorded “some very peculiar signals” from Ross 128. Local radio interference was ruled out as a cause because it did not occur when the telescope listened to other stars.
Other major observatories, the Green Bank Telescope in West Virginia and the Allen Telescope Array in California, were brought in to investigate by the SETI organisation – it stands for the Search for Extraterrestrial Intelligence.
Now a European telescope in Chile has spotted a temperate, Earth-sized planet which orbits its red dwarf star, Ross 128, once every 9.9 days. It is much closer to its sun than Earth is to our own Sun, but because the star is much cooler, temperatures are similar. Ross 128 b’s equilibrium temperature is estimated to lie between -60° and 20°C.
Ross 128 b is now the second-closest temperate planet to be detected after Proxima b, orbiting Proxima Centauri, 4.5 light-years away. But it is considered a more suitable place to look for life because its star is quieter than Proxima Centauri which emits deadly flares of ultraviolet and X-ray radiation.
An international team of scientists used a planet-seeking instrument called HARPS – the High Accuracy Radial velocity Planet Searcher – at La Silla Observatory in Chile, operated by the European Southern Observatory.
ESO said yesterday: “It is also the closest planet to be discovered orbiting an inactive red dwarf star, which may increase the likelihood that this planet could potentially sustain life.”
The new planet will be a prime target for ESO’s Extremely Large Telescope, currently under construction in Chile, because it will be able to search for signs of life known as “biomarkers” in the planet’s atmosphere if it has one.
Speculation that the radio broadcast, dubbed the Weird! signal, was from E.T. was dampened by the radio telescope team. They concluded that it was probably produced by one or more communications satellites which sit in fixed positions high above the Earth. Such satellites are said to be in geostationary orbits.
Professor Méndez said: “The best explanation is that the signals are transmissions from one or more geostationary satellites. This explains why the signals were within the satellite’s frequencies and only appeared and persisted for Ross 128; this star is close to the celestial equator where many geostationary satellites are located.”
Professor Méndez said the explanation did not yet explain certain patterns in the signals, but these might have been caused by “multiple reflections”.
He added in a blog post: “Many people were more interested in the signals as potential proof of transmissions from an extraterrestrial intelligent civilization.
“Statistically, this is always the last consideration, not because such civilizations are impossible, we humans are an example, but because other possibilities had frequently arisen and no extraterrestrial civilizations have been detected yet. Nevertheless, scientists need to be open to all possibilities and explore them.”
However, SETI investigators look set to turn their attention to the Ross 128 star system again in the light of the discover of an Earth-sized world.
In the Berkeley SETI Research Center’s Breakthrough Listen blog, project scientist Danny Price writes: “So sadly, we’ve already looked closely at Ross 128 and have come up empty. Nonetheless, as Ross 128b is such an exciting target, we are considering additional, deeper observations at radio and optical wavelengths.
“Nearby exoplanets are particularly exciting from a SETI perspective as they permit us to search for and potentially detect much weaker signals than from more distant targets.”
The discovery of the new planet is reported in a paper entitled “A temperate exo-Earth around a quiet M dwarf at 3.4 parsecs”, by X. Bonfils et al., to appear in the journal Astronomy & Astrophysics.
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