The internet’s gone wild about a SETI signal from aliens. Scientists aren’t convinced.
Yesterday, the internet lost its mind over the news that Russian astronomers had detected a spike in radio signals, appearing to come from the vicinity of a sunlike star known as HD 164595. The star is just 94 light years away and is known to have one Neptune-like planet.
The media quickly speculated about aliens: “Not a Drill: SETI Is Investigating a Possible Extraterrestrial Signal From Deep Space,” noted the Observer. “If the signal is truly from an alien world, it’s one far more advanced than ours.” Twitter ran wild with the news.
Scientists, however, are far, far more skeptical. Astronomers detect curious radio signals like these fairly often. They usually turn out to be nothing. Sometimes the signal is simply due to natural causes — like a stellar flare, say — or a false positive caused by interference here on Earth. For evidence of extraterrestrial life, scientists would need multiple detections and far more evidence than is available here.
In other words, hold off on planning the UFO welcome parties.
SETI scientists are skeptical that this radio signal is all that interesting
Eric Korpela, an astronomer with Berkeley SETI (as in the “Search for Extraterrestrial Intelligence”), downplayed the hype over this latest signal in a note. “All in all, it's relatively uninteresting from a SETI standpoint,” he wrote:
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, [other astronomers] will look at it. … And we'll all find nothing. It's not our first time at this rodeo, so we know how it works.
In a helpful follow-up post, Korpela explained what sort of signal qualities would convince astronomers that they’re dealing with possible extraterrestrial intelligence:
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.
Unfortunately the observing method used by the Russian team does not permit many of these things to be determine. 1) The signal was not persistent. 2) The signal was gone when the target was reobserved. 3) The signal frequency/period/delay cannot be determined. 4) The signal Doppler drift rate is unknown. 5) Many sources of interference, including satellites, are present in the observing band.
Follow-up investigations have not revealed anything interesting so far
The signal from the direction of HD 164595 was originally discovered in May 2015 by a team in Russia but, oddly, it was only shared with other researchers this month. Since then, other astronomers have tried to confirm the signal. But so far, they haven’t found any follow-up evidence that might suggest they’re onto something.
Here’s Seth Shostak, a senior astronomer with the SETI Institute: “[T]he Allen Telescope Array (ATA) was swung in the direction of HD 164595 beginning on the evening of August 28. According to our scientists Jon Richards and Gerry Harp, it has so far not found any signal anywhere in the very large patch of sky covered by the ATA.”
Scientists at Berkeley SETI also used their instruments to try to follow up on the signal. So far, nothing: “While absence of evidence for extraterrestrial intelligence is by no means evidence of absence, our [telescope] observations did not detect ongoing emission from the direction of HD 164595.”
For now, Shostak writes, “The chance that this is truly a signal from extraterrestrials is not terribly promising … Nonetheless, one should check out all reasonable possibilities, given the importance of the subject.”
A signal that strong from HD 165695 would take an enormous amount of energy to generate
As a fascinating side note, Shostak also calculated that if a signal of the strength supposedly seen by the Russian team did originate from an alien civilization, it would require a staggering amount of energy to generate:
[W]e 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.
That last bit is worth repeating. HD 164595 is 94 light years away — which means that any TV or radar signals we’ve been sending out from Earth haven’t had time to reach them just yet (since they weren’t around 94 years ago). If there was an advanced civilization near that star, it’d have little reason to suspect we’re here.
So tamp down the excitement. With any luck, aliens really are out in the universe, somewhere. But this signal doesn’t seem to be compelling evidence of that.
Further reading: Scientists now think we could find aliens in our lifetimes. Here’s how.