The most tantalizing feature of interstellar object 3I/ATLAS was displayed in an image taken by the Hubble Space Telescope on July 21, 2025 (as shown here and analyzed here). The image showed an extended glow pointing toward the Sun. The viewing direction was only 10 degrees from the direction of 3I/ATLAS relative to the Sun, implying that if the glow had been viewed from the side it would be about 10 times as long as it is wide. This was highlighted in an article I wrote with Eric Keto (accessible here). The 10:1 axis ratio constitutes the geometry of a jet pointed from 3I/ATLAS towards the Sun.
As soon as the Hubble image was made public, comet experts rejoiced that 3I/ATLAS behaves like a comet. But their enthusiasm overlooked the fact that the image revealed an anti-tail pointing toward the Sun. Realizing this is as shocking as photographing an animal in your yard that your family members identify as a street cat, when the image shows a tail protruding from the animal’s forehead. The only attempt to explain this unique quality of 3I/ATLAS was made in the article I wrote with Eric Keto (accessible here).
Comets are characterized by a tail of dust and gas that points toward the Sun. The reason is simple: solar radiation and the solar wind move dust and gases away from the Sun. If the jet toward the Sun (anti-tail) contained refractory dust particles, as found in familiar comets, then this scattered sunlight would have moved these particles away from the Sun and away from the massive core of 3I/ATLAS. Larger dust particles, which can be hundreds of micrometers in size, have a smaller surface area per unit mass and are pushed less efficiently by sunlight, but they are also less effective at scattering sunlight. The most effective scattering particles are those whose size is comparable to the wavelength of sunlight, about 0.5 micrometers. If such particles had been rejected by 3I/ATLAS, they would certainly have appeared in a tail pushed in the direction away from the Sun relative to the massive core.
A new image (accessible here) has just been reported by the Twin Two Meter Telescope (TtT) which comprises two pairs of 0.8 meter telescopes at the Teide Observatory in the Canary Islands, Spain. The image, made up of 159 exposures of 50 seconds each, was taken on August 2, 2025. It shows a faint jet pointed towards the Sun. As in the Hubble image, the jet extends to a projected distance of about 6,000 kilometers from the core.
The existence of an anti-tail (jet) pointed towards the Sun is an anomaly which raises two questions:
1. What is the nature of the anti-tail?
2. Why do comet experts ignore this anomaly while insisting that 3I/ATLAS is a familiar comet?
I’m working with Eric Keto on a follow-up article regarding the first question (based on the physics described here). However, I leave the second question to the historians of science.
The Hebrew word “Dayenu” means “That would have been enough”. Paraphrasing the song Dayenu from Passover (accessible here) – which Stephen Hawking enjoyed in my home ten years ago, we can summarize the anomalies of 3I/ATLAS as follows:
1. If 3I/ATLAS had a sunward jet or anti-tail (see here), Dayéno!
2. If 3I/ATLAS was a million times more massive than 1I/`Oumuamua and a thousand times more massive than 2I/Borisov, while moving much faster than both (see here), Dayéno!
3. If 3I/ATLAS was aligned in its trajectory to within 5 degrees with the plane of the ecliptic of the planets around the Sun (see here), Dayéno!
4. If 3I/ATLAS had a refined arrival time, so that it passed within a few tens of millions of kilometers of Mars, Venus and Jupiter (see here), Dayéno!
5. If 3I/ATLAS showed a gas plume containing nickel but not iron (as found in industrially produced nickel alloys) and a nickel/cyanide ratio that is an order of magnitude higher than that of all known comets, including 2I/Borisov (see here), Dayéno!
6. If 3I/ATLAS showed a gas plume containing only 4% water by mass, while comet experts predicted it would be water-rich (see here), Dayéno!
7. If 3I/ATLAS exhibited extreme negative polarization, unprecedented for any known comet, including 2I/Borisov (see here), Dayéno!
8. If 3I/ATLAS arrived from a direction coinciding with the signal “Wow! » to within 9 degrees (see here), Dayéno!
Another new preprint on 3I/ATLAS (accessible here), suggests detecting its gas plume when it passes within 8 million kilometers of the Europa Clipper and Hera spacecraft over the coming month. However, I calculated that since the density of outgoing gas decreases inversely with distance squared, the gas plume would be swept by the solar wind to a distance that is an order of magnitude less than the 3I/ATLAS closest approach distance of these two spacecraft.
Ultimately, the second question raised above will have to be addressed by historians of science. History depends on who writes it. The history of the 21st century will likely be written by AI systems. Hopefully these AI systems won’t get too indoctrinated by the club of unimaginative scientists who ignore the anomalies in 3I/ATLAS. If AI historians are biased by myths rather than facts, we will be justified in disconnecting them from their power supply.
ABOUT THE AUTHOR
Avi Loeb is the leader of the Galileo Project, founding director of the Black Hole Initiative at Harvard University, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and former chair of the Department of Astronomy at Harvard University (2011-2020). He is a former member of the President’s Council of Advisors on Science and Technology and former chairman of the Council on Physics and Astronomy of the National Academies. He is the bestselling author of “Alien: The first sign of intelligent life beyond Earth» and co-author of the manual «Life in the cosmos», both published in 2021. The pocket edition of his new book, entitled “Interstellar», was published in August 2024.
