Late last August, news spread on the Internet that the Russian radio telescope RATAN-600 had detected a powerful and intriguing signal from the star HD 164595, a heavenly body similar to the Sun in the constellation of Hercules, some 94 light years from us. The announcement, released on the blog Centauri Dreams from the information provided by the Italian astronomer Claudio Maccone, a collaborator of the RATAN-600, spoke of a signal that is unusual for being a natural source. And it was natural that there was an immediate wave of speculation about a possible alien origin.
And it was not just speculation: the SETI Institute (the Search for Extraterrestrial Intelligence) in California immediately directed its Allen Telescope Array (ATA) towards HD 164595, but it did not succeed in hearing any signal. Several SETI projects in different parts of the world point their radio telescopes to the sky hoping to capture a radio signal whose characteristics may reveal an artificial source, such as a repeating pattern or a strong pulse without an apparent natural cause. Scientists look for signals that might be targeted to us by civilizations aware of our existence, but they also search for transmissions that could simply escape into space, like our television signals.
In the case of the RATAN-600 signal, Russian astronomers rushed to publish a note confirming the use of the telescope for SETI searches, but at the same time cooling the excitement over the signal actually detected more than a year earlier, in May 2015: “Subsequent processing and analysis of the signal revealed its most probable terrestrial origin.”
Series of false alarms
The Russian signal is the latest in a long series of false alarms in the half-century history of SETI, an effort that was at its birth already linked to unfulfilled expectations: the first search, on April 8, 1960, detected a possible sign that turned out to be a spy plane. With the exception of the so-called Wow! signal, captured on August 15, 1977, which still has not been provided with an irrefutable explanation, all the others have been natural phenomena or human interference, sometimes of the most unexpected nature. In 2015, the Parkes observatory in Australia finally managed to locate the source of some enigmatic pulses in their own kitchen; they were coming from the microwave used by the scientists to heat their food.
Another high-profile current case is the star KIC 8462852 some 1,500 light years from Earth. In October 2015, The Atlantic revealed that astronomers were astonished by the aberrant behavior of this star, unofficially called Boyajian’s star or Tabby’s star, after the name of the Yale researcher who noticed the phenomenon, Tabetha Boyajian. Over several years of observation, the Kepler space telescope had recorded a sporadic and reversible attenuation of the brightness of the star by 22%, an amount impossible to attribute to the transit of a planet. Neither could it be the disk of material that can surround a young star, since KIC 8462852 seemed to be a mature star.
When the data came to the knowledge of astrophysicist Jason Wright at Penn State University, he connected Boyajian’s data with one of his lines of work, the possibility of detecting alien civilizations. If a highly advanced technological species build a swarm of large engineering structures in orbit around its star, the result would be something similar to what was observed in the case of Boyajian, the partial concealment of light. In the 1960s, physicist Freeman Dyson formalized this idea that was already making the rounds in science fiction circles, and thus these hypothetical structures became known as Dyson spheres, rings or swarms.
Since then, Boyajian’s star has continued to generate controversy, and both interest and skepticism. The SETI scans have not been able to find any radio signal or laser pulse from the star. Subsequent studies supported the hypothesis proposed by Boyajian and her collaborators: the attenuation of the star could be due to the passage of a cloud of debris from the fragmentation of a family of comets. However, this theory capsized when further investigation suggested that the light from the star had reduced in total by some 20% over the last century, something that did not fit the hypothesis of a transitory passage of comet fragments.
Although these data were then questioned by another study, the fact is that there appears to be a trend of attenuation over time that does not fit with the idea of comets. A new analysis of Kepler data released last August has discovered that the star lost 3% of its brightness during the four years of observation. “No known or proposed stellar phenomena can fully explain all aspects of the observed light curve,” the authors of the study concluded.
Wright proposed as the most plausible hypothesis that the attenuation is not due to something around the star, but rather something very far away: materials that incidentally fall into our line-of-sight, such as interstellar dust and gas. At the same time that Wright proposed his idea, two US astronomers were detailing the possible presence of a swarm of interstellar material, formed of comets and planetoids, in the line-of-sight of the star.
Searching for life beyond Earth
Perhaps future observations will come to elucidate the enigma of Boyajian’s star. But whether this happens or not, the case illustrates that the search is no longer only based on radio or optical signals. As David Black, President and CEO of the SETI Institute, commented to OpenMind, “we could infer the presence of aliens by virtue of what they do to their planet.” Or to their star. And whatever the final verdict on the mysterious star turns out to be, “the recent false alarms, and the large amount of press attention they have gotten, demonstrate how profound an endeavor SETI is and how much public interest there is in this topic,” says astrophysicist Andrew Siemion, director of the Center Berkeley SETI Research to OpenMind.
“We have now determined conclusively that the principal environmental conditions necessary for life to begin on Earth, a temperate rocky planet, water and organic chemistry, exist ubiquitously throughout the galaxy,” says Siemion. “This discovery has provided a surge of motivation for all kinds of searches for life beyond Earth, including SETI.” The astrophysicist hopes this new interest is also reflected in public funding of projects.
In short, one could say that these are good times for the search for signs of alien life, despite the inevitable false alarms. And precisely where the first false alarm occurred on April 8, 1960, at the Green Bank telescope in West Virginia, next week Siemion and his team will try to hear a signal from Boyajian’s star. And with the same enthusiasm of the first day, without giving in to discouragement: “We’re very excited.”