Imagine a comet with an unexpected abundance of nickel, defying everything we thought we knew about these icy travelers. New data from the European Very Large Telescope in Chile has revealed a startling mystery surrounding the interstellar object 3I/ATLAS. A recent report (available here: https://arxiv.org/pdf/2509.26053) highlights an anomalous concentration of nickel and iron in the gas plume enveloping this cosmic visitor. But here's where it gets controversial: these metals shouldn't be there.
Comets, with their frigid surfaces, are too cold to vaporize the minerals that contain nickel and iron. Yet, 3I/ATLAS not only contains these elements but does so in a ratio that dwarfs what we see in our own solar system’s comets. For context, the nickel-to-iron ratio in 3I/ATLAS is an order of magnitude higher than the typical cometary ratio. Even the interstellar comet 2I/Borisov, which made headlines in 2019, didn’t exhibit such extremes.
The data, collected over six time intervals as 3I/ATLAS approached the Sun, shows nickel present consistently, while iron only appeared at closer distances. This peculiar behavior raises more questions than answers. As the authors of the study aptly put it, the presence of these metals in a cometary coma is “extremely puzzling.”
And this is the part most people miss: 3I/ATLAS isn’t just any comet—it’s a C2-depleted comet, meaning it lacks certain organic compounds typically found in comets. This makes its extreme nickel production even more baffling. What’s causing this? Is it a natural phenomenon, or could there be another explanation?
Looking ahead, we’re in for a treat. Between October 1–7, 2025, NASA’s Mars Reconnaissance Orbiter and ESA’s Mars Express and ExoMars will observe 3I/ATLAS as it swoops within 29 million kilometers of Mars. The HiRISE camera on the Mars Reconnaissance Orbiter will capture images with a resolution of 30 kilometers per pixel—far superior to the Hubble Space Telescope’s recent snapshot taken from 570 million kilometers away. These images could reveal the comet’s true size, which I’ve estimated to be larger than 5 kilometers—wider than Manhattan Island.
Speaking of size, here’s a mind-boggling comparison: the first interstellar object, 1I/'Oumuamua, was just 0.1 kilometers across, about the size of a football field. Why is 3I/ATLAS a million times more massive? The upcoming observations might shed light on this discrepancy, or they could deepen the mystery. Nature, it seems, is full of surprises.
Science thrives on these unexpected discoveries, challenging us to rethink what we know. Recently, I received an email from a former US Air Force pilot whose daughter, inspired by my discussion of 3I/ATLAS on television, now dreams of becoming a scientist. Moments like these remind me why this work matters.
During a recent appearance on Fox & Friends, I was asked whether 3I/ATLAS could be a technological artifact rather than a natural comet. My response? While it’s most likely natural, we must remain open to the possibility of a “black swan event”—a cosmic anomaly that defies our expectations. After all, the NSF-DOE Rubin Observatory is scanning the skies for interstellar objects, and who’s to say one of them might not be something entirely unexpected?
What do you think? Could 3I/ATLAS hold secrets beyond our current understanding, or is it simply a natural oddity? Share your thoughts in the comments—let’s keep the conversation going.
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. A former chair of Harvard’s astronomy department (2011–2020), he has also served on the President’s Council of Advisors on Science and Technology. His bestselling books, Extraterrestrial: The First Sign of Intelligent Life Beyond Earth (2021) and Interstellar (2024), explore the frontiers of cosmic discovery. His latest work, Interstellar, is now available in paperback.
