The Wow! Signal Revisited: Citizen Science Informs SETI Effort

As far as interesting problems go, few can really compete with the perennial question: “Are we alone?” The need to know if there are other forms of intelligent life out there in the galaxy is deeply rooted, and knowing for sure either way would have massive implications.

But it’s a big galaxy, and knowing where to look for signals that might mean we’re not alone is a tough task. Devoting limited and expensive resources to randomly listen to chunks of the sky in the hopes of hearing something that’s obviously made by a technical civilization is unlikely to bear fruit. Much better would be to have something to base sensible observations on — some kind of target that has a better chance of paying off.

Luckily, a chance observation nearly 50 years ago has provided just that. The so-called Wow! Signal, much discussed but only occasionally and somewhat informally studied, has provided a guidepost in the sky, thanks in part to a citizen scientist with a passion for finding exoplanets.

No really — Wow!

We’ve already covered the story of the Wow! Signal and how we got to this point in the story, but to summarize: in 1977, a radio telescope in Ohio known as “The Big Ear” detected an unprecedented signal coming from the general direction of the constellation Sagittarius. As the fixed antenna swept the night sky thanks to the rotation of the Earth, a stream of radio noise entered the dual feed horns of the instrument, with a signal-to-noise ratio that peaked at over 30 times the typical background noise. The signal, which lasted 72 seconds, became known as the “Wow! Signal” thanks to astronomer Jerry Ehman’s excited note from the night of August 15, made in red pen on the margin of the fanfold hard copy of the data.

In the 45 years since that night, the Wow! Signal has been at the center of a storm of scientific curiosity. In some ways, it bears all the hallmarks of being a transmission from another technical civilization. The frequency of the signal was very close to the 1,420-MHz hydrogen line frequency, and anyone capable of building a radiotelescope would most likely know about that frequency and might choose to use it in their efforts to search for other life in the galaxy. The signal’s characteristics were also very much in line with what one would expect for an extraterrestrial beacon, given the rotational speed of the Earth at the latitude of the antenna. There have also been extensive efforts to provide alternative explanations for the signal, none of which have ruled out an extraterrestrial signal.

Then again, there hasn’t been much to support the Wow! SIgnal’s potential as an extraterrestrial calling card either. No other observatories working that night picked up anything similar, and multiple attempts to listen to the patch of sky for a repeat of the event have failed to hear a peep. Forty-five years on, the Wow! Signal remains the worst kind of event, scientifically speaking: a one-off, a chance observation that provides a tantalizing clue for more work, but nothing more.

Citizen Science Points the Way

And yet, scientists are still plugging away at the Wow! Signal, since it seems to be the best chance we’ve had so far to find out who might be out there. One such scientist is Alberto Caballero, an amateur astronomer from Spain who, as head of the Habitable Exoplanet Hunting project, very much has extraterrestrial life on his mind. The project enlists astronomers, both pros and amateurs, to turn their telescopes to the stars in search of faint dimming events that might result from planets passing in front of the star. The project focuses its efforts on a small group of G-type, K-type, and red dwarf stars within 100 light-years of Earth, and looks for transit signals that would be characteristic of rocky exoplanets within the habitable zone around each star.

2MASS 19281982-2640123, a Sun-like star within the Wow! Signal footprint. Source: Alberto Caballero.

Alberto’s interest in exoplanets took a different turn with a paper he published this year concerning a potential source for the Wow! Signal. The peer-reviewed paper suggests that out of 66 stars that were within the view of the Big Ear’s feedhorn on that night in 1977, the star 2MASS 19281982-2640123 may be a good candidate for further investigation, by virtue of its luminosity and size.

Picking up on this thread, a group of astronomers led by Karen Perez of Columbia University recently made the first coordinated, multi-telescope observations of 2MASS 19281982-2640123, with the specific intent of locating a “technosignature” from the star. Using the Green Bank Telescope in West Virginia and the SETI Institute’s Allen Telescope Array in northern California. The team coordinated observations so that both telescopes were looking at the target star at the same time, and made their observation at the same 1,420-MHz frequency of the original Wow! Signal.

Sadly, the experiment resulted in no technosignature, perhaps not a surprise since the total time that both telescopes were trained on the star was only nine minutes or so. But the effort is still significant, mainly because it’s the first time in the 45 years since the Wow! Signal was heard that a coordinated observation effort has been undertaken. Such an effort can only make it easier to coordinate observations of spurious signals, both as they pop up and after the fact. It also suggests other candidates besides 2MASS 19281982-2640123 — they found that there are actually eight Sun-like stars in the observation window used by the Big Ear that night; relaxing the criteria for luminosity, mass, and star type opens the candidate pool substantially, to over 600 stars.

There’s certainly more to come on this and other SETI efforts, and while we look forward to hearing how they turn out, for now we’re glad that a little citizen science has proven to be the foundation upon which a much broader effort has been built.

[Featured image source: North American Astrophysical Observatory.]

52 thoughts on “The Wow! Signal Revisited: Citizen Science Informs SETI Effort

  1. >1,420-MHz hydrogen line frequency

    Why would a civilization try to contact another using a frequency that is exactly at the frequency of background noise in the universe? Everything that has hydrogen in it makes noise at that frequency.

    1. Hm, one reason could be because it’s some sort of a fix point. A frequency marker to listen to.

      Any space faring civilization could also try to send/listen on a frequency that’s being absorbed by water/atmosphere. Milimeterwaves, so to say.

      1. Some cultures use pi 3.14 and some use 2pi 6.28 even here on earth. Some engineers prefer 1/pi 0.3183 and then there are other constants like e 2.7182.
        Then again these numbers only exist because we have a base-10 math system, because humans have 10 fingers.
        Which one would you use?
        Would you multiply or divide?

        1. Pi is an irrational number and cannot be expressed as a ratio of two integers in any base.

          But then again, almost all real numbers are irrational. There’s nothing special about Pi.

          1. Nope, infinitely more irrationals than rationals. Cantor proved this (there are uncountably many irrationals, where ‘countable’ means ‘can map these to natural numbers’) back in 1874.

            It’s not *super* hard to understand this. Just think of square roots of primes, all of which are irrational and unique. Take any rational number times that square root, and it’s still irrational. So you’ve got an entire copy of the rationals right there. But any *other* square root of a prime also has that same thing… and they’re all unique, too.

            The more formal argument is called Cantor’s diagonalization proof, and it’s like, one of the masterpieces of modern mathematics.

        2. “Then again these numbers only exist because we have a base-10 math system,”

          Numbers themselves have nothing to do with the base used to express them. The base just provides a method for representing them with symbols.

          The original suggestion (“hydrogen*pi”) originates both from Sagan’s book, as well as SETI’s early days, apparently independently. It has the benefit that the signal cannot be generated from harmonics of the original frequency since it’s irrational.

          1. But then, because the universe is expanding, the signal would be doppler-shifted and you wouldn’t know what the original was unless you also knew where what made it and where it’s coming from.

          2. Uh, by the time you have to worry about doppler shift from the Universe expanding, it means you’re sending out signals with equivalent power to a friggin’ galaxy. So… I think you can find other ways to deal with it.

          3. Well, that would be the problem with aliens sending a signal that was recognizable on earth with a 1977 radio telescope anyways. The source of it would have to be enormously powerful – like a “friggin galaxy” – to even register.

            It’s got everything going against it, like the hydrogen line frequency being blocked by the ionosphere and interference from our own sun, etc.

          4. No. Not even remotely close. Any civilization in the Milky Way could do it if they’re advanced enough. They’re close. That always wins.

            Cosmological redshift happens on many megaparsec scales before you even would change it by a tenth of a percent. You don’t see individual stars at that point.

          5. > Any civilization in the Milky Way could do it

            And that’s the other problem. Sagittarius A is in the direction to the center of our galaxy, which is a strong source of radio noise at these frequencies.

          6. “Sagittarius A is in the direction to the center of our galaxy”

            Sag A* is a radio source that’s 52 microarcseconds in size. Method for avoiding: don’t look in that direction.

            Seriously, you’re massively off in scale here. Astronomers use the 21 cm line to track neutral hydrogen because the emissions from other stuff in that region are generally very weak. Cuz hydrogen ain’t neutral in stars.

            Go take a look at the sky in 21 cm. It was on APOD oh, 25+ years ago. No stars. Just diffuse gas. And it’s not that strong, because it’s velocity broadened and not a sharp peak.

            This is not a real significant concern.

      1. Computers used mostly text terminals back then, and those are signal strengths represented as printable alphabet. Guess zeros were not printed, there are some 1 from time to time, and this hump.

    2. “that is exactly at the frequency of background noise in the universe?”

      The background noise of the universe is the cosmic microwave background, not the 21-cm line. You could actually make the argument that it might be smart for an intelligent civilization to send a message at the 21-cm line *in the receiver’s frame*, which would both be a technological signature *and* an indicator that the message was meant for the receiver.

      The problem with doing something like “pi*hydrogen” is that there are a bunch of “natural” options there. Frequency times pi, frequency times 2 pi, wavelength times pi, wavelength times 2 pi, etc. Plus, of course, they might not be that enamored with pi in the first place: it’s elementary school math, after all. So maybe it’s frequency times e, or wavelength times e…

      1. That’s not exclusive. The cosmic microwave background is the leftover from the big bang – there are other radio sources in the universe that count as “background noise” when you’re looking for intentional signals.

        The Sun being the closest.

        1. Point being, all you need is a high altitude mylar weather balloon drifting up somewhere up the sky near dawn or dusk, and whoops there’s your radio reflection of a 21-cm noise signal coming from the sun. It is a difficult frequency to use because everywhere you have ionized hydrogen, you get that radio signal, and even a tiny leak becomes a “Wow” signal when you’re expecting picowatts per square kilometer from some distant celestial source.

          1. In the 1970s, with a single dish? Sure.

            Nowadays, with multi-kilometer baseline interferometry? No way. Interference is a pain in the neck, sure, but you don’t get fooled by silly things like that. Scientists map things using the 21 cm line, after all.

            Look, the “Wow!” signal thing’s a fun story, but we all know it wasn’t a real ET signal. But the methods aren’t crazy.

            Most importantly, if you’re announcing your presence on the 21 cm line… you don’t just do it once.

  2. SETI is a massive waste of effort and money that would have paid much greater dividends if focused on other areas of research. The I part of SETI is basically a fraud as even if there was an interesting signal detected the required interaction needed to prove that it is intelligent (Turing Test) is not likely to be possible and otherwise complex patterns or mathematical sequences can easily be generated via relatively simple gravitational automata such as the clusters of interacting black holes and their associated jets at the center of many galaxies. Even narrowband signals can be formed by gravitational lensing as you only see the part of the spectrum that has diverged in your direction.

    1. RF SETI is pretty much a joke. Unless a civilization is willing to stupidly use a very high power directional beam to broadcast its presence into space, effectively into an “unknown neighborhood,” no one will detect them. Spectral analysis of atmospheric gases is a better way.

      Dr Seth Shostak answers your questions about SETI (2005)

      Q: What is the maximum distance at which SETI can detect signals which are not deliberately beamed at us, such as normal radio telecommunications traffic?

      A: Our best SETI experiments to date could detect Earth-like “leakage” signals at no more than 1 light-year’s distance. So not too far.

      Aliens can’t hear us, says astronomer [so, we can’t hear them]
      Fainter broadcasting signals and digital switchover mean Earth will soon be undetectable to extraterrestrials

    2. SETI’s annual budget is about $2.5mil which is less than it costs US taxpayers every time the president goes golfing on the weekend.

      As long as that money keeps 75-100 people gainfully employed, SETI is okay in my book.

  3. Closer to home, there was a fairly recent paper about objects seen in high Earth orbits on old astronomical photographic plates, objects which should still be there, but aren’t. The significance is that these were there before humans put anything in orbit. I’ve stupidly lost the link to that paper and the article which sent me looking for it.

  4. No matter what it is, it is originated from a very long time ago because it’s source is very far away and since we detected something, it has to fit within our knowledge of how things behave. So far we don’t do FTL travel and AFAIK, hasn’t repeated

  5. What if for say a year all the amateur radio astronomers agree to train their antennas on that patch of sky for at least 10 minutes whenever they do an observation session. You’d likely get a nice body of data (yes, yes far from perfect but statistically better than one 10-minute snapshot). Or is this all beyond amateur radio astronomy?

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