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Image: RATAN-600 telescope
SETI researchers say an intriguing radio spike was detected last year by the RATAN-600 radio telescope. (Credit: SAO RAS)

SETI researchers are buzzing about a strong spike in radio signals that seemed to come from the direction of a sunlike star in the constellation Hercules, known as HD 164595.

The signal conceivably fits the profile for an intentional transmission from an extraterrestrial source – but it could also be a case of earthly radio interference, or a microlensing event in which the star’s gravitational field focused stray signals coming from much farther away.

In any case, the blip is interesting enough to merit discussion by those who specialize in the search for extraterrestrial intelligence, or SETI – including Centauri Dreams’ Paul Gilster, who brought the case into the public eye this weekend.

At least two SETI research groups are aiming to track HD 164595 tonight. The SETI Institute is using the Allen Telescope Array in northern California, while METI International is looking to the Boquete Optical SETI Observatory in Panama.

Gilster reports that the signal spike was detected more than a year ago, on May 15, 2015, by the RATAN-600 radio telescope in Zelenchukskaya. That facility is in the Russian republic of Karachay-Cherkessia, not far from the Georgian border.

The apparent source of the signal, HD 164595, is interesting for a couple of reasons: It’s a sunlike star, about 95 light-years away from Earth, and it’s already known to have at least one “warm Neptune” planet called HD 164595 b. “There could, of course, be other planets still undetected in this system,” Gilster says.

The case has been compared to the one-time-only “Wow Signal” of 1977, or the more recent controversy over KIC 8462852, also known as “Tabby’s Star” or the alien-megastructure star.

There’s been no word of a sequel to HD 164595’s blip in the more than 15 months since it was recorded. Nevertheless, Gilster says it’s due for discussion at next month’s International Astronautical Congress in Mexico.

The researchers behind the detection, led by Nikolai Bursov of the Russian Academy of Sciences’ Special Astrophysical Observatory, rate HD 164595 as a good candidate for SETI investigation. “Permanent monitoring of this target is needed,” they say.

Doug Vakoch, president of San Francisco-based METI International, said his research group would try observing HD 164595 as early as tonight, weather permitting, with the Boquete Optical SETI Observatory. In an email to GeekWire, he explained why he and other SETI scientists have an obligation to follow up on intriguing prospects:

“Standard SETI protocols call for confirmation of possible signals from a separate observatory. This helps ensure that the original signal didn’t arise from a technical glitch in the original observatory, and it helps rule out a hoax perpetuated by some enterprising graduate students targeting a SETI experiment.

“In the past, plans for SETI follow-up observations have focused on confirmation of the original signal, seeking a repeat signal at the same frequency. That’s a critical step for confirmation – and we don’t yet have evidence that this sort of follow-up has happened for HD 164595.

“In addition, we need to be alert to the possibility than if we do really find a signal from an advanced civilization, they are also transmitting at other frequencies than the one where we first detected them. That’s why it’s so important to prepare for follow-up SETI observations at both radio and optical frequencies, to be launched as soon as we detect a credible candidate signal at any frequency.”

Vakoch was involved in follow-up observations of KIC 8462852 last year, and he plans to keep watch on Proxima Centauri as well.

Update for 9:30 p.m. PT Aug. 28: Seth Shostak, senior astronomer at the SETI Institute in Mountain View, Calif., weighed in on HD 164595 in an email to GeekWire:

“This is a bit of a puzzling story, as the Russians found this signal a year ago or so, but just didn’t let others know. That’s not good policy, as what you really want is confirmation at another telescope, but… Is it real?  The signal may be real, but I suspect it’s not ET.  There are other possibilities for a wide-band signal such as this, and they’re caused by natural sources (or even terrestrial interference).

“I just did a quick calculation of how much wattage they’d need to wield from 94 light-years (I think that’s the distance) in order to produce the apparently received signal, and that would be a big utility bill, even if they were directing the transmission (as opposed to broadcasting equally in all directions).  It’s also the case that the known planet around the star is in an awfully tight orbit, which means it’s probably a place that’s hotter than Seattle’s best restaurant.  Of course, there could be other planets there …

“So, not too much to say so far.  However, we’re looking at this object with the Allen (not Alan) Telescope Array as I speak to you!”

Check out Gilster’s full report about HD 164595 on Centauri Dreams, and be sure to read the comments.

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