Imagine spotting a comet with a tail pointing directly at the Sun. It sounds impossible, right? Yet, that's exactly what astronomers observed with the interstellar object 3I/ATLAS, captured in a stunning image by the Hubble Space Telescope on July 21, 2025. This bizarre feature, resembling a jet aimed sunward, has sparked both fascination and controversy in the scientific community. But here's where it gets even more intriguing: this so-called 'anti-tail' defies everything we thought we knew about comets.
Comets, as we understand them, have tails of dust and gas that are pushed away from the Sun by solar radiation and wind. So, how can 3I/ATLAS have a tail pointing toward the Sun? It’s like discovering a cat with a tail growing out of its forehead—utterly baffling. In a paper co-authored with Eric Keto (available here), we explored this anomaly, revealing that the jet’s 10:1 axis ratio suggests a structure unlike anything seen in typical comets.
When the Hubble image was released, comet experts were quick to label 3I/ATLAS as just another comet. But their enthusiasm overlooked the glaring contradiction: the anti-tail. If this jet contained the same refractory dust particles found in ordinary comets, solar radiation should have pushed them away from the Sun, not toward it. Even larger dust particles, though less affected by sunlight, would still scatter light in a way that would make a sunward tail impossible. And this is the part most people miss: the absence of a conventional tail in the image further challenges the idea that 3I/ATLAS is a typical comet.
A new image from the Two-meter Twin Telescope (TtT) at the Teide Observatory in Spain, taken on August 2, 2025, confirms this anomaly. Composed of 159 exposures, it shows a faint jet extending 6,000 kilometers toward the Sun—mirroring the Hubble findings. This raises two critical questions:
1. What is the nature of this anti-tail?
2. Why are comet experts dismissing this anomaly while insisting 3I/ATLAS is a familiar comet?
I’m currently working with Eric Keto on a follow-up paper addressing the first question, but the second is a matter for historians of science. Speaking of history, the Hebrew word Dayenu—meaning “It would have been enough”—perfectly encapsulates the anomalies of 3I/ATLAS. Let’s break it down:
- If 3I/ATLAS had a sunward jet, Dayenu!
- If it were a million times more massive than 1I/'Oumuamua and a thousand times more massive than 2I/Borisov, Dayenu!
- If its trajectory aligned within 5 degrees of the ecliptic plane, Dayenu!
- If it passed within tens of millions of kilometers of Mars, Venus, and Jupiter, Dayenu!
- If its gas plume contained nickel but no iron, with a nickel-to-cyanide ratio far exceeding known comets, Dayenu!
- If it showed only 4% water by mass, contrary to predictions, Dayenu!
- If it exhibited extreme negative polarization, unseen in any comet, Dayenu!
- If it arrived from a direction just 9 degrees off the “Wow! Signal”, Dayenu!
Adding to the intrigue, a recent preprint suggests detecting 3I/ATLAS’s gaseous plume as it approaches the Europa Clipper and Hera spacecraft. However, my calculations show that the solar wind would sweep away the plume long before the spacecraft get close enough to detect it.
Ultimately, the second question—why experts ignore these anomalies—will be left to historians. And with AI systems likely writing the history of the 21st century, we must hope they prioritize facts over myths. If not, we might just have to unplug them.
About the Author:
Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s Black Hole Initiative, and director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics. He is the bestselling author of Extraterrestrial: The First Sign of Intelligent Life Beyond Earth and co-author of Life in the Cosmos. His latest book, Interstellar, was published in August 2024.
Now, here’s a thought-provoking question for you:
Is 3I/ATLAS a comet, an alien artifact, or something entirely new? Share your thoughts in the comments—let’s spark a discussion!
