Was the “Wow! Signal” Emitted from 3I/ATLAS?

Medium ^ | Avi Loeb

[RoosterRedux]

The “Wow! Signal” was detected on August 15, 1977 as a strong narrowband radio signal by Ohio State University’s Big Ear radio telescope. Its origin was inferred to be extraterrestrial. The latest natural explanation (accessible here) hypothesized that the “Wow! Signal” was caused by a sudden brightening of the hydrogen line emitted from an interstellar cloud, triggered by a strong transient radio source, such as a flare from a highly magnetized neutron star (magnetar).

The “Wow! Signal” originated from the sky coordinates of Right Ascension (RA)=19h25m=291 degrees and Declination (Dec)=-27 degrees.

On August 12, 1977, the interstellar object 3I/ATLAS was at a distance of about 600 times the Earth-Sun separation (AU) — corresponding to a light-travel time of about 3 days. It had the sky coordinates of RA=19h40m=295 degrees and Dec=-19 degrees. These parameters can be inferred accurately given the lack of non-gravitational acceleration for 3I/ATLAS, as inferred in my latest paper (accessible here).

Hence, the “Wow! Signal” was separated by approximately 4 degrees in RA and 8 degrees in Dec from the direction of 3I/ATLAS. The chance of two random directions in the sky being aligned to that level is about 0.6 percent. If the “Wow! Signal” originated from 3I/ATLAS, how powerful was the transmitter?

The detected intensity of the “Wow! Signal” was in the range of 54–212 Jansky with a bandwidth of about 10 kilohertz. At the distance of 600 AU, this corresponds to a source power of 0.5–2 gigawatts, the output of a typical nuclear reactor on Earth.

The “Wow! Signal” was observed at a frequency of 1420.4556±0.005 megahertz, blue-shifted by about 10 kilometers per second towards Earth relative to the central frequency of the hydrogen line. This blueshift is of the same order of magnitude but smaller than expected from the approach velocity of 3I/ATLAS towards the Sun, 60 kilometers per second.

So far, no radio telescope reported data on 3I/ATLAS. Here’s hoping that the coincidence in the arrival direction of 3I/ATLAS and the “Wow! Signal” would motivate radio observers to check whether 3I/ATLAS shows any radio transmission around the hyperfine line of hydrogen.

Path of 3I/ATLAS as of September 25, 2025 relative to planets and space missions. (Credit: Space Initiatives) This raises a broader question: in case we detect an artificial signal from an interstellar object, how should we engage with it?

The details would depend on the properties of the object. To measure these properties, we should attempt to use all telescopes on Earth and in space.

Between October 1–7, 2025 NASA’s Mars Reconnaissance Orbiter and ESA’s Mars orbiters Mars Express and ExoMars will observe 3I/ATLAS as it passes within 29 million kilometers from Mars. Subsequently, between November 2–25, 2025, ESA’s Jupiter Icy Moons Explorer (Juice) will observe 3I/ATLAS with various instruments.

The urgency of a response would depend on the rank of the object on the Loeb Scale (see the quantitative discussions here and here). Rank 10 would suggest an imminent threat akin to a visitor to our backyard who is capable of approaching the front door, requiring an immediate response. But even a low rank would necessitate a contingency plan because of the major implications to humanity if the threat is realized. We must consider the possibility of a black swan event from interstellar objects resembling a comet at large distances, but potentially carrying devastating consequences to our future like a Trojan Horse.

Our engagement could either be messaged electromagnetically through a radio or laser communication signal, or involve interceptors which cross the path of the interstellar object, land on it or take a close-up photograph.

Our interpretation of the data would be biased by our limited knowledge. In analogy with artificial intelligence (AI) systems, human reasoning is as good as its training data set. Whereas our knowledge is restricted to experiences on Earth, our dating partner might exhibit alien designs which go well beyond our current perception of reality. In that case, communication might be as difficult as it is for ants looking from the vantage point of a crack in a pavement at a biker passing by.

ABOUT THE AUTHOR

(Image Credit: Chris Michel, National Academy of Sciences, 2023) Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. The paperback edition of his new book, titled “Interstellar”, was published in August 2024.

[PJ-Comix]

Meanwhile Ellie Arroway is still sitting in the same New Mexico radio telescope field for almost thirty years, wearing headphones and waiting, waiting, WAITING to hear her own interstellar “WOW!” signal.

[dangus]

>> Hence, the “Wow! Signal” was separated by approximately 4 degrees in RA and 8 degrees in Dec from the direction of 3I/ATLAS. <<

So, the answer is No.

4 and 8 degrees means “no way near” in astronomical terms.

>> The chance of two random directions in the sky being aligned to that level is about 0.6 percent.<<

And the chance that 4 degrees equals 0 degrees is 0 percent. However, the chance of finding something with a 0.6% probability among a hundred billion events is several hundred million.

[DoodleBob]

Wow! Is really fascinating and easy to understand if the lecturer doesn’t try to be the Smartest Guy in the Room. I’ll try- YMMV.

In short, there was a view that any extraterrestrial civilization attempting to communicate via radio signals might do so using a frequency of 1420 megahertz (21-centimeter spectral line), which is naturally emitted by hydrogen, the most common element in the universe and therefore likely familiar to all technologically advanced civilizations.

To test that view, Ohio State University assigned the now-defunct Ohio State University Radio Observatory (nicknamed "Big Ear") to the scientific search for extraterrestrial intelligence (SETI). The observatory ingested radio signals and printed out large amounts of data processed by an IBM 1130 computer and recorded on line printer paper.

This is the computer printout in question.

The signal intensity was measured as signal-to-noise ratio, with the noise (or baseline) averaged over the previous few minutes. The signal was sampled for 10 seconds and then processed by the computer, which took 2 seconds. The result for each frequency channel was output on the printout as a single alphanumeric character, representing the 10-second average intensity, minus the baseline, expressed as a dimensionless multiple of the signal's standard deviation. (Standard deviation is a statistical measure of variation.)

In this particular intensity scale, a space character denoted an intensity between 0 and 1, that is between baseline and one standard deviation above it. The numbers 1 to 9 denoted the correspondingly numbered intensities (from 1 to 9); intensities of 10 and above were indicated by a letter: "A" corresponded to intensities between 10 and 11, "B" to 11 to 12, and so on. The Wow! signal's highest measured value was "U" (an intensity between 30 and 31), which is thirty standard deviations above background noise.

Here is a different way of displaying the values.

I hope that helps.

[P.O.E.]

Looks like wow and flutter.

/(old fogey tape recorder reference mode)

[P.O.E.]

Looks like wow and flutter.

/(old fogey tape recorder reference mode)

[BigFreakinToad]

Moon Nazi’s, it’s always Moon Nazi’s.

[GingisK]

Apollo era spacecraft transmitters were never very strong. The Apollo Command Module transmitter was only 5 watts. That is why those huge dish and horn ground station antennas were used. I imagine the telemetry transmitters and transponders on the boosters were not any stronger.

[yesthatjallen]

"Was the “Wow! Signal” Emitted from 3I/ATLAS?"

No.

[MarlonRando]

yeah I’m familiar with the signal it’s just that the universe is a big place, and we know next to nothing about what is out there, so unless something is blatantly obvious, I don’t know. I’m sure there is a mountain range on a planet somewhere that looks like dolly Parton

[Charles Martel]

Looks like wow and flutter.

Someone figured out how to play that golden record on the Voyager probe?

[PJ-Comix]

So that explains why Ellie Arroway has been sitting in a New Mexico Radio Telescope field for almost 30 years. She has been trying to listen to the Code 6EQUJ6 11 1 signal when all this time it was the Code 6EQUJ5 11 1 signal she should have been tuned in to.

[DoodleBob]

Well done and yes. It’s all about variation off a baseline.

FWIW, tape is making a modest comeback. The kidz think it’s cool.

[SunkenCiv]

The rest of the Wow Signal keyword, sorted:

• Astronomers Revisit the Mysterious Wow! Signal -- and Find a Big Surprise [meh] [08/26/2025]
• SETI breakthrough! NASA scientist discovers three repeating ET signals coming from nearby stars! [19:57] [06/24/2025]
• Double telescope study of zone where Wow! signal originated comes up empty [11/29/2022]
• Amateur astronomer Alberto Caballero finds possible source of Wow! signal [11/25/2020]
• What Was the WOW Signal? [09/21/2015]
• Is this ET? Mystery of strange radio bursts from space [04/01/2015]
• SETI's Colossus (Huge 77-meter infrared telescope) [05/31/2013]
• Possible alien message to get reply from humanity [06/26/2012]
• Interstellar Signal from the 70s Continues to Puzzle Researchers (WOW signal) [12/05/2002]

[dangus]

I was actually familiar with Wow!, but I can still appreciate that you gave an excellent, quick summary/explanation of it.

[Hatteras]

Haha, yes. It would be a little more interesting perhaps, if they explained in English what a “Wow signal” is...

[cgbg]

“there was a view that any extraterrestrial civilization attempting to communicate via radio signals might do so using a frequency of 1420 megahertz (21-centimeter spectral line), which is naturally emitted by hydrogen”

It sounds like witch doctors hiding behind science.

It uses wild assumptions—unsupported by any real world data—about what an ET would do.

I hope that helps.

[fidelis]

Someone figured out how to play that golden record on the Voyager probe?

"Send more Chuck Berry!!

[PIF]

New “coincidental” anomaly for 3I, on top of all of the other “coincidental” anomalies: It will or already had been it by a CME.

Only a few comets have ever been observed being hit by a CME. Its anti-tail should be blown away, and its nascent trail also blown away when the CME hits. The tail should reform quickly.

Next up is the 18 million mile approach to Mars; after that it is supposed to go behind the Sun on the 29th. We will not know what it does until a few days later, but it is supposed to head on for a close approach to Jupiter next March.

The coming days will indicate what sort of object it really is. But if its trip into the solar system is any indication - hold on to your hat, the ride may be bumpy.

[logi_cal869]

[Political Junkie Too]

Where's the kaboom? there was supposed to be an earth-shattering kaboom!

-PJ