Hold up, alien hunters. Extraterrestrial signal may not be that interesting after all

Aug 30, 2016 - 8:28pm AST

The Internet went into a frenzy yesterday after news surfaces that astronomers discovered a mysterious and strong signal coming from HD 164595.

HD 164595 is a star just 94 light years away and is about 6.3 billion years old with one planet orbiting around it.

The signal was detected via the RATAN-600 radio telescope in Zelenchukskaya, Russia back in May 2015. The news was initially kept secret and passed around to select agencies, before Paul Gilster broke the news to the wider community.

The news was then passed on to SETI (Search for Extraterrestrial Intelligence) for further analysis, where one astronomer deemed the discovery to be nothing noteworthy.

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In a post on the SETI forums, astronomer Eric Korpela from Berkeley SETI, was ‘unimpressed’ with the findings.

I was one of the many people who received the the email with the subject “Candidate SETI SIGNAL DETECTED by Russians from star HD 164595 by virtue of RATAN-600 radio telescope.” Since the email did come from known SETI researchers, I looked over the presentation. I was unimpressed. In one out of 39 scans that passed over star showed a signal at about 4.5 times the mean noise power with a profile somewhat like the beam profile. Of course SETI@home has seen millions of potential signals with similar characteristics, but it takes more than that to make a good candidate. Multiple detections are a minimum criterion.

Because the receivers used were making broad band measurements, there’s really nothing about this “signal” that would distinguish it from a natural radio transient (stellar flare, active galactic nucleus, microlensing of a background source, etc.) There’s also nothing that could distinguish it from a satellite passing through the telescope field of view. All in all, it’s relatively uninteresting from a SETI standpoint.

But, of course, it’s been announced to the media. Reporters won’t have the background to know it’s not interesting. Because the media has it, and since this business runs on media, everyone will look at it. ATA is looking at it. I assume Breakthrough will look at it. Someone will look at it with Arecibo, and we’ll be along for the ride. And I’ll check the SETI@home database around that position. And we’ll all find nothing. It’s not our first time at this rodeo, so we know how it works.

Even with the announcement, many sources were initially skeptical because the signal was only detected once with no other telescopes being able to confirm the findings.

Korpela followed up with criteria used in determining signals of interest.

We believe a signal when

  • It is persistent. It appears at the same spot in the sky in multiple observations.
  • It only comes from one spot in the sky.
  • If we reobserve the target, the signal is still there.

Things that add to believability

  • Its frequency/period/delay does not correspond to known interference.
  • Its Doppler Drift rate indicates that it is exactly frequency stable in the frame of the center of mass of the solar system
  • Its properties (bandwidth, chirp rate, encoding) indicate intelligent origin.

When the news initially broke, many speculated that transmitting a signal 94 light years away would require an insanely high amount of energy, only capable of a Kardashev Type II civilization. As a result, many went on to believe that there was an actual possibility of the existence of a Dyson Sphere.

This was also ‘ruled’ out in another SETI post, this time written by Senior Astronomer, Seth Shostak.

Now note that we can work backwards from the strength of the received signal to calculate how powerful an alien transmitter anywhere near HD 164595 would have to be. There are two interesting cases:

(1) They decide to broadcast in all directions. Then the required power is 1020 watts, or 100 billion billion watts. That’s hundreds of times more energy than all the sunlight falling on Earth, and would obviously require power sources far beyond any we have.

(2) They aim their transmission at us. This will reduce the power requirement, but even if they are using an antenna the size of the 1000-foot Arecibo instrument, they would still need to wield more than a trillion watts, which is comparable to the total energy consumption of all humankind.

Both scenarios require an effort far, far beyond what we ourselves could do, and it’s hard to understand why anyone would want to target our solar system with a strong signal. This star system is so far away they won’t have yet picked up any TV or radar that would tell them that we’re here.

This does not mean that alien life may not be a myth, but there is little to no evidence to prove that this signal is simply nothing more than interference. You’ll have your day, Dr. Arroway.

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