A new paper on the interstellar object 3I/ATLAS (accessible here), reports data taken by the Keck II telescope in Hawaii on August 24, 2025, when 3I/ATLAS was at distances of 2.75 and 2.6 times the Earth-Sun (AU) separation from the Sun and Earth, respectively. As with the Hubble Space Telescope image obtained on July 21, 2025 (analyzed here and here), the image taken by the Keck Cosmic Web Imager (KCWI) in the wavelength range of 0.3425 to 0.55 micrometers shows evidence of a puzzling anti-tail extension toward the Sun.
Unlike all known comets, including the interstellar comet 2I/Borisov, the spectrum of the gas plume observed around 3I/ATLAS shows significant nickel emission but no trace of iron. With the exception of 3I/ATLAS, this anomaly only existed in nickel alloys produced industrially by the chemical carbonyl route, which refines nickel by the formation and decomposition of nickel tetracarbonyl, Ni(CO)4. The authors of the new article postulate that this carbonyl process occurs naturally near the core of 3I/ATLAS. They argue that “this in situ formation of Ni(CO)4 predicts that nickel should be highly concentrated near the core.”
A narrow-band KCWI image of 3I/ATLAS emitting nickel (Ni) and cyanide (CN) in the wavelength ranges 0.3865 to 0.3885 and 0.3605 to 0.3625 micrometers respectively, shows a central concentration of nickel relative to cyanide. Emissions from the surrounding gas plume extend over an exponential radius of 600 kilometers for nickel and 840 kilometers for cyanide.
Describing another anomaly, the authors claim that “the rate of nickel production relative to cyanide is higher than in 2I/Borisov and several orders of magnitude above the median for Solar System comets.”
The nickel and cyanide emission profiles around 3I/ATLAS are asymmetric with extension in the solar and anti-solar directions, providing clear evidence of an anti-tail. Even more remarkable, the 3I/ATLAS white-light image shows no trace of a familiar cometary tail, as would be expected for dust that scatters sunlight and is pushed away from the Sun by the pressure of solar radiation.
The above data add new anomalies to the classification of 3I/ATLAS as a familiar comet. The more data we get from 3I/ATLAS, the more this looks like an outlier. Considering the previous seven anomalies of 3I/ATLAS (as summarized here), I keep its rank at 4 on the Loeb scale (as quantified here and here).
We are still awaiting the public release of images taken by the HiRISE camera aboard the Mars Reconnaissance Orbiter on October 2, 2025. The HiRISE images will show a side view of the glow around 3I/ATLAS as it passes within 30 million kilometers of Mars. Its pixel resolution of 30 kilometers will be about 3 times better than our best images obtained so far with the Keck and Hubble telescopes. Additional data on 3I/ATLAS will be provided by the Juice spacecraft in November 2025 and by the Juno spacecraft in March 2026.
There is nothing better than higher quality data to clarify the nature of 3I/ATLAS. Science is fun because it allows us to gain new knowledge from evidence collected by instruments rather than from stories collected by people.
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.
