For several days, a curiously energetic radio signal coming from the stellar system HD 164595 had eager Earthlings wondering whether signs of intelligent extraterrestrial life had finally been discovered.
But follow-up observations with some of Earth’s most prolific alien-hunting telescopes have so far turned up empty: Neither the Allen Telescope Array, commanded by the SETI Institute, nor the Green Bank Telescope, used by the Breakthrough Listen project, detected any signs of a tantalizing signal from this distant world.
That’s not necessarily surprising, given the vague and dubious nature of the original signal (more on that in a minute).
In a translation of a statement posted online on August 30, the Russian Academy of Science notes that, based on their analysis, the signal is most likely of terrestrial origin.
“This is getting blown way out of proportion,” says Andrew Siemion of the University of California, Berkeley.
For nearly 60 years, astronomers have aimed radio telescopes at the heavens, hoping to detect the murmurs of faraway civilizations advanced enough to broadcast radio waves into the cosmos. Over those decades, the search has been not exactly comprehensive, a casualty of scarce resources and sporadic telescope time.
Still, the question of whether extraterrestrials exist is so nagging that possible signals are an all-hands-on-deck situation. Any answer will be profound, whether it’s that we’re alone in this vast universe, or that the cosmos is teeming with chatty aliens.
That’s why this signal, which looked like a pronounced spike of radio waves caught people’s attention. Detected on May 15, 2015, by Russia’s RATAN-600 telescope in Zelenchukskaya, the signal came from a star system about 95 light-years away in the constellation Hercules—the very same constellation that Frank Drake targeted when he sent Earth’s first intentional postcard to the stars in 1974.
The particular star in question is really rather sunlike: It’s got the same basic list of ingredients, is just a smidgen smaller than our home star, is roughly the same age, and has at least one planet, a Neptune-size world in a toasty orbit.
In other words, HD 164595 is exactly the kind of star scientists searching for signs of intelligent life have focused on for years.
But the chances of a civilization being at the other end of this spiky radio signal are small. Almost immediately after the detection surfaced, astronomers looking critically at the signal were skeptical. It didn’t repeat, and it looked like a generic excess of radio power, meaning that several much more mundane explanations were vastly more plausible.
“Their receiver was set up to gobble up a huge chunk of the radio dial at once,” says Seth Shostak, senior astronomer at the SETI Institute. “Generally, SETI looks for narrow-band signals … that's like your laser pointer, which, although it has very little power, makes a highly visible spot because it's all in one wavelength range.”
Other more likely explanations than aliens include a case of radio frequency interference caused by a source on Earth, such as a faulty power supply, military transmission, or arcing electrical fence. Another possibility is that the gravity from a celestial object passing between Earth and HD 164595 amplified an otherwise faint, hardly detectable signal. A third option is that some sort of transient astrophysical source is to blame.
Despite those doubts, the signal begged for further telescope observations. Even in the best-case scenario, a single observation does not equal a detection of sentient alien life. Confirming the presence of intelligent extraterrestrials requires that multiple telescopes detect the same blip. It’s also widely proclaimed that such a detection should be announced immediately and not subjected to the same secrecy and embargoes that often plague scientific discoveries.
So on August 28, the Breakthrough Listen project aimed the Green Bank Telescope at HD 164595—and detected nothing.
“Our GBT observations did not detect ongoing emission from the direction of HD 164595,” the group reports. “Single-epoch transients are by their nature hard to confirm or deny, illustrating the need for confirming follow-up, either at a later time, or as part of the observing strategy.”
Similarly, when the Allen Telescope Array observed the star on August 28 and 29, it detected nothing but silence. According to Shostak, the team failed to find a signal at the frequencies detected by the Russians, and they should have by now if it was indeed as strong as advertised.
“Might be a reprise of the Wow Signal experience, or maybe just interference, given the telescope's weird beam shape,” Shostak muses, referencing a famous SETI signal that made waves in 1977 and continues to fan conspiracy theories. "Mind you, maybe ET went on holiday."
There’s no question that, in an age when humanity is grappling with its own continued existence on Earth, finding signs of intelligent life in the cosmos would be revolutionary. Such a discovery would reshape the ways in which humans view one another and the watery blue sphere we call home. So any tantalizing signal, such as the one from HD 164595, is worthy of intense follow-up observations.
“In the specific case of the search for life beyond Earth, the question itself is so compelling that we ought to always be doing the best possible experiments we can think of to try and find an answer,” Siemion says. “Science is a constant process of chipping away at our ignorance … as long as we have a good idea and experimental means, we should continue to seek answers.”
So who knows? It may not happen this time, or the next time, or the time after that, but if we keep looking, the answer to the question may finally arrive.