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Green Bank Telescope
The Green Bank Telescope in West Virginia is tracking a faraway sunlike star known as HD 164595 for the Breakthrough Listen Initiative. No alien blips have been received so far. (Credit: NRAO)

Fifteen months after an intriguing radio signal was picked up from a sunlike star in the constellation Hercules, follow-up observations over the past couple of days have so far yielded nothing notable.

That shouldn’t be too surprising. It’s the way things have always turned out so far in the 56-year history of the radio search for extraterrestrial intelligence, known as SETI.

Nevertheless, the focus on a star called HD 164595 has served as a teachable moment for those interested in the search.

“Our follow-up observations of HD 164595 remind us of the importance of developing the organizational infrastructure that will let SETI research groups around the world communicate easily with one another, so interesting signals can get a fast follow-up observation from an independent site,” Doug Vakoch, president of METI International, told GeekWire in an email.

Back in May 2015, Russian researchers using the RATAN-600 radio telescope picked up a strong spike at the 11 GHz radio frequency, bearing the signature of a point-like transmission source. They traced the source to the vicinity of HD 164595, 94 light-years away.

It wasn’t until a few weeks ago that word about the detection filtered out to SETI researchers, in preparation for next month’s International Astronautical Congress in Mexico. And it wasn’t until last weekend that the report came into the public eye.

Since then, the SETI Institute has been checking up on HD 164595 using the Allen Telescope Array in California, while the Breakthrough Listen Initiative is employing the Green Bank Telescope in West Virginia. Both groups say they’ve detected no signals worthy of note.

In a preliminary report, the Breakthrough Listen team says last year’s transient radio flash was so bright that it’s unlikely to have been caused by a natural astrophysical phenomenon. “The question in our mind is, why aren’t we seeing things like this all over the sky?” team member Steve Croft, an astronomer at the University of California at Berkeley, told GeekWire.

That suggests that the Russian researchers were “either extremely lucky to detect this source in their observations, or that the transient is due to local interference or other calibration issues,” the team said. Interference could have come from an earthly source (even a microwave oven) or a satellite passing overhead.

The SETI Institute and Breakthrough Listen have added HD 164595 to the list of thousands of stars that they monitor for anomalous signals, including nearby prospects as well as stars known to have potentially habitable planets.

It wouldn’t be surprising if last year’s blast was a one-off occurrence, similar to the “Wow Signal” that apparently emanated from somewhere in the constellation Sagittarius in 1977. If that’s what happens to HD 164595, Vakoch advises that we should let it fade away:

“Assuming we don’t find any evidence of a transmitting civilization as we conduct follow-up observations, the worst outcome would be to turn HD 164595 into another Wow signal – seen once, never confirmed, but lurking in the imagination as perhaps really a message from another world. Unless we can observe another similar signal from the vicinity of this star, we need to dismiss the May 2015 signal as a spurious result, and not wishfully hope it was really from ET.”

But that doesn’t mean SETI researchers should just go back to square one. Vakoch’s organization, for instance, is trying to set up a network of modest-sized telescopes capable of spotting anomalous flashes of light in optical wavelengths.

One such telescope, the Boquete Optical SETI Observatory, has been primed in Panama to observe HD 164595, but so far the weather hasn’t been cooperating.

SETI groups are also looking into ways to work more closely together on follow-up observations. And by October, Breakthrough Listen expects to bring the Parkes Telescope in Australia online for SETI observations. Croft said that will eventually boost the team’s target list from thousands of stars to a million.

Croft said he and his colleagues are also talking about setting up a rating scale for SETI cases, based on the existing Rio Scale. “We’re thinking about ways in which we might be able to quantify the significance of claims like this,” he said, referring to the claims made for HD 164595.

Such a scale would serve the same purpose that the Torino and Palermo scales serve for potential asteroid threats. The Torino Scale for asteroid risk assessment goes from 1 to 10, and so far, no case has ever risen above Level 4.

The Rio Scale also goes from 1 to 10, and by my reckoning, HD 164595 rates a 3.

Will anything ever crank the dial up to 11? Probably not – but whether it’s aliens or asteroids, it’s still a good idea to keep watching the skies.

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