According to new data reported in a paper that was posted today on the arXiv, 3I/ATLAS exhibits “reddening colors … with no visible tail detected.” The authors explain these features as being “likely due to viewing geometry and low dust production.”
When I argued in an essay on July 20, 2025 that the prematurely claimed elongation in the images of 3I/ATLAS might be an artifact resulting from the motion of the object, I was attacked by bloggers which insisted that it represents evidence for a cometary tail. Now that the dust has settled, literally speaking, we can ask again: could 3I/ATLAS be something other than a comet?
This possibility is not discussed in the new paper. The concluding sentence of the paper’s abstract states: “Continued monitoring around perihelion is necessary to track changes in activity, color, which will provide insights into the evolution of interstellar materials under solar radiation.” I wholeheartedly agree with this imperative for a simple reason. The more data we collect, the more difficult it would be for scientists to shove anomalies of 3I/ATLAS under the carpet of traditional thinking. We are used to finding icy rocks which exhibit familiar cometary tails in the solar system, but an encounter with objects from interstellar space is a blind date on astronomical scales.
The newly inferred rotation period of 16.16 hours for 3I/ATLAS is still not statistically robust, since it was derived from an observing time window spanning only 1.5 spin periods and so it may suffer from the well-known Shannon-Nyquist uncertainty in information theory.
Recent days led to a rise in the number of commentators who, despite not being practicing scientists, are ready to unequivocally denounce non-cometary interpretations of the data on 3I/ATLAS. The truth will be revealed in the coming couple of months as 3I/ATLAS gets closer to the Sun and its anomalies will be easier to measure. If it continues to be deficient of carbon-based molecules or a visible cometary tail, will comet experts argue that it is a dark comet as they suggested recently for 1I/`Oumuamua?
Let me reiterate a point which is avoided by these commentators. In my first published paper on 3I/ATLAS, I showed that a rock as wide as 20 kilometers — as inferred from the brightness of 3I/ATLAS, can only be delivered from interstellar space into the inner solar system once per 10,000 years. Yet, we discovered 3I/ATLAS over the past decade. Moreover, as shown in a second paper that I wrote with Adam Hibberd and Adam Crowl, the retrograde trajectory of 3I/ATLAS is fined tuned to be in the ecliptic plane (with a probability of 0.2%), and its arrival time is fine tuned to get unusually close to Jupiter, Mars and Venus (with a probability of 0.005%). I was asked in television and radio interviews this morning (including those here and here) to rank 3I/ATLAS on the `Loeb scale’ where `0’ is a definitely natural object and `10’ is a definitely technological object. As of now, I give 3I/ATLAS a rank of 6, but noted that this rank will be time-dependent as it reflects the limited data we have so far. Asking the question: `Is 3I/ATLAS alien technology?’ should not be censored for the simple reason that we must avoid being misguided by prejudice. In science, any question is legitimate, including whether COVID-19 came from a lab leak in the Wuhan Institute of Virology rather than the Huanan wet market. The scientific method allows for all possible questions, which are later answered by collecting data and ruling out possibilities. It is anti-scientific to suppress curiosity-driven questions about anomalies before conclusive data is gathered to explain them.
The spectroscopic data reported in the new paper on 3I/ATLAS, as well as in three previous papers (here, here and here), does not show the features expected for atomic or molecular gas in a coma. The observed reddening in the spectrum of reflected sunlight from 3I/ATLAS is commonly interpreted as dust, but it could also be associated with a red surface for the object.
A puzzling development on social media is that advocates for the Search for Extraterrestrial Intelligence (SETI) or Unidentified Anomalous Phenomena (UAP) are both pushing back against the possibility that 3I/ATLAS might be alien technology. This resistance is contradictory to their defining commitment to be curious and agnostic about all anomalies that might be associated with extraterrestrial technologies. Gladly, this resistance has no impact on my ongoing scientific research, as I already wrote four scientific papers on 3I/ATLAS (accessible here, here, here, and here).
All in all, the verdict will be up to data and not opinions voiced on social media. Science is fun as long as we remain open minded and view it as a learning experience and not as a tool for virtue signaling.
Over the past day, new figures were added to the latest paper I wrote a week ago with Adam Hibberd and Adam Crowl, which suggested to probe 3I/ATLAS with the Juno spacecraft when it passes within a distance of 54 million kilometers from Jupiter on March 16, 2026. The new figures show that two impulses of thrust can bring Juno to within 10 million kilometers from the path of 3I/ATLAS, using merely 60 kilograms of propellant, only 3% of the initial fuel that Juno had at its disposal. Here’s hoping that NASA will follow on our proposal for the benefit of interstellar space archaeology. The scientific exploration of our cosmic neighborhood is young and we still have a lot to learn.
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.