Discovered on July 1, 2025, by the Chilean station of the ATLAS project (Asteroid Terrestrial-impact Last Alert System), the interstellar comet 3I/ATLAS entered the inner Solar System at a distance of approximately 670 million kilometers from the Sun, immediately drawing attention for its unusual characteristics. The name “3I” indicates that it is the third recorded interstellar object, following ‘Oumuamua (2017) and 2I/Borisov (2019).
Since its discovery, 3I/ATLAS has been challenging traditional knowledge about comets, displaying a series of intriguing anomalies that are forcing scientists to rethink their theories. The most notable include:
- Unexpected chemical composition: Analyses from the James Webb Space Telescope revealed that its “atmosphere” (coma) has a carbon dioxide (CO₂) to water ratio much higher than that observed in any Solar System comet, suggesting it may have formed under very different conditions, possibly in a CO₂ ice-rich region of its original stellar system.
- “Antitail” or plume pointing toward the Sun: Unlike most comets, which have tails pushed away from the Sun by the solar wind, 3I/ATLAS exhibits a plume pointing toward the Sun, a rare phenomenon that may be related to its rotation or surface changes over billions of years.
- Brightness vs. nucleus paradox: Although it shines intensely, suggesting a large object, observations from the Hubble Space Telescope indicate that its solid nucleus is relatively small and dark, a contradiction that continues to puzzle astronomers.
- Low water content: James Webb also detected surprisingly low levels of water in its coma, reinforcing the idea that its composition is atypical compared to comets known in our Solar System.
These peculiarities make 3I/ATLAS a true interstellar mystery, an object that could reveal secrets about planetary system formation beyond our own and challenge established concepts of comet physics and chemistry.
The most recent study, conducted with the Very Large Telescope in Chile, adds a new layer of mystery to 3I/ATLAS by revealing something even more surprising: the presence of nickel without iron in the gas plume surrounding the comet. Interestingly, this combination is typical of industrial processes used to manufacture metal alloys, rather than natural formations known in space.
Normally, natural comets contain both iron and nickel, as these elements are formed simultaneously in supernova explosions. The absence of iron in this case challenges our traditional understanding of the composition of interstellar celestial bodies, solidifying 3I/ATLAS as one of the most enigmatic objects ever observed.
This discovery raises even more intriguing questions about the possible origin of 3I/ATLAS. The study suggests that the observed chemical formation may occur through the nickel carbonyl pathway, an extremely rare and exotic process in natural comets, but a standard technique in industrial nickel refining.
Analysis of the gas plume showed that the comet loses about 5 grams of nickel per second at a distance of 2.8 astronomical units from the Sun, a rate that increases sharply as it approaches the star, following a power-law index of -8.43 (±0.79). In addition, cyanide (CN) was detected, with a mass loss rate of approximately 20 grams per second and an even stronger heliocentric distance dependence, raised to a power of -9.38 (±1.2).
These findings add to observations made by SPHEREx and the James Webb Space Telescope, which revealed that the plume of 3I/ATLAS is composed of 95% CO₂ and only 5% water, in stark contrast to typical water-rich comets. The apparent discrepancy between the size of the nucleus and the amount of reflected light suggests two possibilities: either an extremely dense dust coma reflects nearly all sunlight, forming a tail that, curiously, was not observed, or most of the light is reflected by the nucleus itself, making 3I/ATLAS a million times more massive than 2I/Borisov.
Another surprising aspect is the precise alignment of the comet’s trajectory with the ecliptic plane of the planets, which raises the hypothesis that it could have deliberately targeted the inner Solar System, reinforcing speculations about a potentially technological origin.
