First Limit on Technological Radio Transmission from 3I/ATLAS | by Avi Loeb | Nov, 2025
The MeerKAT radio telescope in South Africa conducted on November 5, 2025 a search for narrowband radio transmission from the interstellar object 3I/ATLAS using the commensal backend BLUSE suitable for a real-time search for radio technological signatures. As reported here, a total of 23,689 signals were detected; however, all were determined to not be spatially consistent with the position of 3I/ATLAS and thus were likely caused by human-made radio frequency interference. From these observations, the observers established a detection limit of 0.17 Watts over the frequency range of 900 to 1670 megahertz, approximately equivalent to the power output of a mobile phone handset at the distance to 3I/ATLAS, which was 334 million kilometers at the time.
Today at 3PM ET, NASA will broadcast a press conference here in which new data from ground-based and space-based observations will be publicly released for the first time after the government shutdown. The data will include images of 3I/ATLAS when the object came within 29 million kilometers from Mars on October 3, 2025. At that time, the HiRISE camera onboard the Mars Reconnaissance Orbiter could have imaged 3I/ATLAS with a pixel resolution of 30 kilometers.
The brightest pixel in the HiRISE image would constrain the nucleus size and reveal the geometry of the glow around it. It is also interesting to check if there is any evidence for new objects that either accompanied 3I/ATLAS or left it towards Mars. They could imply fragments from an iceberg that broke up or mini-probes released by a technological mothership.
The fundamental question looming in the background remains: “Is 3I/ATLAS a rare comet of a type never seen before or a technological object?” So far, 3I/ATLAS did not display any unambiguous technological signatures, such as a major maneuver, artificial light or transmission of a radio signal.
Below is a recap of the anomalies of 3I/ATLAS that could flag a technological signature:
1. Its trajectory opposite to the direction of motion of the planets is aligned to within five degrees with the ecliptic plane of the planets around the Sun, with a likelihood of 0.2 per cent (see here). This suggests that the trajectory may have been designed for a reconnaissance purpose.
2. During July and August as well as in early November of 2025, it displayed a sunward jet (anti-tail) that is not an optical illusion from geometric perspective, unlike familiar comets (see here). This might be a technological signature.
3. Its nucleus is about a million times more massive than 1I/`Oumuamua, an interstellar object discovered in 2017, and a thousand times more massive than 2I/Borisov, discovered in 2019, while moving faster than both, altogether with a likelihood of less than 0.1 per cent (see here and here). This suggests that it may have targeted the inner solar system rather than being drawn from the reservoir of icy rocks.
4. Its arrival time was fine-tuned to bring it within tens of millions of kilometers from Mars, Venus and Jupiter and be unobservable from Earth at perihelion, with a likelihood of 0.005 per cent (see here).
5. Its gas plume contains much more nickel than iron (as found in industrially-produced nickel alloys) and a nickel to cyanide ratio that is orders of magnitude larger than that of all known comets, including 2I/Borisov, with a likelihood below 1 per cent (see here). This may be a signature of industrial production of its surface.
6. Its gas plume contains only 4 per cent water by mass, a primary constituent of familiar comets (see here).
7. It shows extreme negative polarization of light, unprecedented for all known comets, including 2I/Borisov, with a likelihood below 1 per cent (see here). This might be a technological signature.
8. It arrived from a direction coincident with the radio ‘Wow! Signal’ to within 9 degrees, with a likelihood of 0.6 per cent (see here). This might imply that the `Wow! Signal’ may have originated from it or its senders.
9. Near perihelion, it brightened faster than any known comet and was bluer than the Sun (see here). Perhaps this is a signature that its engine turned on.
10. It exhibits jets in the direction of the Sun and opposite to it, which require an unreasonably large surface area in order to absorb enough sunlight needed to sublimate enough ice to feed the mass flux of these jets (as calculated here). Perhaps the jets originate from technological thrusters.
11. Near perihelion it exhibits non-gravitational acceleration which requires massive evaporation, whereas preliminary images indicate that the object maintained its integrity and did not break up (as discussed here). Perhaps the acceleration was produced by an engine.
12. Its tightly-collimated jets maintain orientation across a million kilometers in multiple directions relative to the Sun despite its measured rotation (as discussed here). This might imply that they are used for navigation or associated with the release of mini-probes from a mothership.
If an interstellar object happens to be technological, it could pose a threat to humanity. A few months ago, I described the `Loeb Scale’ (as quantified here and here) — where a rank of `0′ implies a natural comet and a rank of `10′ corresponds to alien technology that threatens humanity. We do not have a response protocol for alien technology, but after the first encounter — as long as we survive it — there will be political will to invest trillions of dollars in a warning system of interceptors that take close-up photos of anomalous interstellar objects. 3I/ATLAS is expected to arrive closest to Earth at a distance of 269 million kilometers on December 19, 2025. Let us hope that it will not deliver us any unwanted gifts for the holidays.
Among the unexpected gifts I received today was the following uplifting message:
“Mr. Loeb,
I have been following your work, interviews and published papers since September and just wanted to express to you my immense gratitude for you! You are a rare and incredible person as you’re not only a phenomenally brilliant scientist, but such a humble person who truly desires to share truth with all people, not for your own benefit but for the benefit of all people. Your determination in the face of great challenges and undeserved scrutiny has been remarkable and admirable to witness.
You have reignited my love for and fascination with science. I’m a Realtor/regular working Mom and don’t work in science or engineering but every day I look forward to checking your publications. I have to admit that for someone like me, in full transparency, many of the high level (yet fascinating) concepts/details in your papers require a much higher level of thought than I possess, and yet you somehow find a way to make the key points understandable for us non-scientists (which is no easy task lol).
Even more important than science, you’ve taught me that there are still truly good people in the world who refuse to be corrupted by power, riches or pride. Thank you for sharing your brilliance, carrying yourself with grace, being courageous (when I’m sure it would be much much easier not to), and for sharing truth and making it accessible to all people. Your incredible work will be remembered throughout history!
Warm regards,
Angelique Jones”
ABOUT THE AUTHOR
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.
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