New observations of the interstellar comet 3I/ATLAS have revealed the latest in a growing collection of anomalies the object displays, deepening the mystery surrounding its unusual composition and possible origins.
The latest data, obtained during observations with the Keck II telescope in Hawaii, offer the latest confirmation of the existence of the object’s strange “anti-tail” and unexpected chemical signatures that reveal it is rich in nickel, yet seemingly devoid of iron, in contrast to past observations of comets.
The new findings, detailed in a recent paper based on Keck Cosmic Web Imager (KCWI) data collected on August 24, 2025, suggest that 3I/ATLAS could be showing signs of exotic chemical processes currently unfamiliar to astronomers.
A key finding from the new data also confirms the presence of a nickel-carbonyl formation process, which on Earth is normally associated with industrial nickel refinement. This adds to past findings that suggest the object could be chemically unique among all known comets observed to date, and could provide deeper insights into the composition and chemical behaviors of comets and other space objects from beyond our solar system.
A Deepening Mystery
The latest findings, part of an international effort led by researchers at the University of Hawaiʻi at Mānoa in Honolulu, Hawaii, examined KCWI spectral observations in the wavelength range of 0.3425 to 0.55 micrometers collected by the Keck telescope in August. These revealed what appears to be a distinctive plume of nickel emission that now surrounds 3I/ATLAS, while still showing no signs of iron.
The ongoing observations of 3I/ATLAS, which lack iron, contrast sharply with past observations of comets, including comet Borisov, the second known interstellar object observed by astronomers. This is significant, as currently, such a singular abundance of nickel without iron is associated with the production of nickel alloys.
“Other than 3I/ATLAS, this anomaly was only known to exist in industrially-produced nickel alloys through the carbonyl chemical pathway,” wrote theoretical physicist Avi Loeb, who was not involved with the recent study, but summarized its findings in a post on his Medium page, noting that this process “refines nickel through the formation and decomposition of nickel tetracarbonyl, Ni(CO)4.”
While certainly anomalous, the authors of the recent study propose that the object’s peculiar nickel abundance could result from a similar reaction occurring naturally near the nucleus of 3I/ATLAS, leading to a strong local concentration of nickel.
Mapping Chemicals in the Coma
Narrow-band KCWI images of 3I/ATLAS obtained over the summer captured emissions from both nickel (0.3865–0.3885 µm) and cyanide (0.3605–0.3625 µm), which reveals a central clustering of nickel relative to the cyanide the object displays. A resultant gas plume produced by 3I/ATLAS extends outward to an estimated distance of 600 kilometers for nickel, and up to around 840 kilometers for cyanide.
Based on these observations, the research team calculated trace mass loss rates of 3.9 grams per second for the farther-reaching cyanide portion of the plume, and 0.9 grams per second for nickel, with a total mass loss rate of close to 150 kilograms per second.
“Another anomalous abundance is that of [iron and nickel] relative to H2O,” the study’s authors note. The team’s observations are consistent with other recent observations that suggest the object is spewing water at a rate of up to 40 kilograms per second, which some have compared to water being ejected from a “fire hose at full blast.”
In short, the comet is losing quite a lot of material, and at an unusually high rate. Furthermore, based on data obtained earlier this year by the James Webb Space Telescope, this overall composition consists of roughly 87% carbon dioxide, 9% carbon monoxide, and only 4% water—essentially the opposite of what is typically found in standard comets.
3I/ATLAS Has Grown an Anomalous “Anti-Solar Tail”
Further adding to the intrigue surrounding 3I/ATLAS, the unique emission profiles of the nickel and cyanide it is releasing also appear to be extending in both the solar and anti-solar directions, confirming the presence of an odd “anti-tail” first observed in observations earlier this year.
“3I/ATLAS has indeed developed an anti-solar tail as of late August,” the researchers confirm in their paper. This unusual structure appears to point in the direction of the Sun, whereas in the past, cometary plumes have generally been oriented in the opposite direction.
Curiously, observations have also revealed that there appears to be no visible cometary dust tail in white light images of 3I/ATLAS, suggesting that radiation pressure from the Sun is not a significant driver of the dust emissions astronomers are currently observing from the object.
Altogether, the new Keck II Telescope findings help to place even further distance between 3I/ATLAS and other known comets. Additional clues could be offered with the release of imagery obtained by the HiRISE camera aboard NASA’s Mars Reconnaissance Orbiter, although the current U.S. government shutdown has halted the release of this imagery, along with additional updates from the American space agency related to the object’s current transit of our solar system.
Earlier this month, during the object’s closest approach to Mars, spacecraft operated by the European Space Agency (ESA) successfully captured images of the comet in what it characterized as a “challenging” series of observations. With the eventual release of the HiRISE images, astronomers could be afforded the clearest view of 3I/ATLAS yet seen, offering image resolution nearly three times that of what the Keck and Hubble telescopes have so far captured.
Additional spacecraft observations will follow in the months ahead, with the ESA’s Juice mission targeting the object in November 2025, and NASA’s Juno spacecraft slated for further imaging next March.
In the years ahead, many more observations of interstellar objects like 3I/ATLAS are expected, particularly with the imagery obtained by the Vera C. Rubin Observatory and its Legacy Survey of Space and Time. In their recent paper, the authors predict that this survey “will discover and observe more interstellar comets, especially at greater heliocentric distances.”
“As the number of these objects increases, population-level studies of the metal content in these objects and its dependence on heliocentric distance will be feasible,” they add, “providing new insights into the extrasolar systems in which they form.”
The team’s recent paper, “Spatial Profiles of 3I/ATLAS CN and Ni Outgassing from Keck/KCWI Integral Field Spectroscopy,” by Willem Hoogendam, et al, is currently available on the preprint server arXiv.org.
Micah Hanks is the Editor-in-Chief and Co-Founder of The Debrief. A longtime reporter on science, defense, and technology with a focus on space and astronomy, he can be reached at micah@thedebrief.org. Follow him on X @MicahHanks, and at micahhanks.com.