Interstellar comet 3I/ATLAS, first detected in July 2025, has captivated astronomers and the public alike with its unusual behavior and enigmatic characteristics. Expected to be a typical icy visitor from beyond our solar system—briefly visible as it glowed and shed dust before breaking apart near the Sun—3I/ATLAS has defied these predictions. Instead, it boasts a striking blue-green glow and a tail extending over a million kilometers, and most notably, it survived an extremely close pass behind the Sun in November without fragmenting or weakening. This surprising resilience has reignited a fierce scientific debate, pitting traditional comet theories against more extraordinary explanations.
One of the most vocal proponents of the comet’s unusual nature is Harvard astrophysicist Avi Loeb, known for his controversial investigations into possible extraterrestrial technologies. Loeb highlights new images captured on November 11 by the Nordic Optical Telescope in Spain’s Canary Islands, which show that 3I/ATLAS remained an “active, single body” with no signs of breakup following its perilous solar encounter. For Loeb, this is a key anomaly; the comet’s mass-loss jets—streams of gas and dust ejected from its surface—appear far too powerful relative to its estimated size. He argues that to generate jets of such magnitude, the comet would need an absorbing surface area larger than Manhattan Island, a scale that contradicts all prior observations and conventional comet models.
Delving deeper into the energy dynamics, Loeb analyzed the sunlight energy incident on the comet at perihelion—the closest point to the Sun. According to his calculations, the Sun delivered about 700 Joules per square meter per second, which would require an active absorbing area exceeding 1,600 square kilometers to sustain the observed jet activity. This dimension far surpasses the expected size of a comet nucleus of 3I/ATLAS’s scale, leading Loeb to propose a radical alternative: that 3I/ATLAS is not a natural comet at all. Supporting this hypothesis, he points to unusual structural features such as an anti-tail, a rare phenomenon where the comet’s tail points toward the Sun instead of away from it, which is atypical for cometary physics.
In one of his most provocative suggestions, Loeb proposes that the comet’s intense jets might not be natural outgassing but rather “technological thrusters”—engineered propulsion mechanisms designed to accelerate the object away from the Sun after its close solar passage. This kind of maneuver, he speculates, could be employed by an advanced spacecraft using the Sun’s gravity to gain speed, instead of slowing down as typical gravitational assists do. Such a propulsion system might also explain how 3I/ATLAS survived the intense heat and radiation of the solar encounter intact, rather than disintegrating as most comets do under similar conditions.
However, not all astronomers agree with Loeb’s extraterrestrial interpretation. Professor Darryl Seligman from Michigan State University offers a more conventional perspective, dismissing the idea that 3I/ATLAS is alien technology. He argues that the comet’s survival is consistent with its estimated nucleus size of about one kilometer in diameter, which is relatively large for a comet and could explain its robustness. Seligman suggests that Loeb’s assumptions about the size and strength of the mass-loss jets might be overestimated, and that 3I/ATLAS is displaying behavior typical of a durable comet. From this vantage point, the comet’s intact return after passing close to the Sun is not extraordinary but rather within the expected range for such objects.
Further bolstering the natural comet theory is a significant detection made by South Africa’s MeerKAT radio telescope. On October 24, MeerKAT observed radio absorption lines attributed to hydroxyl radicals—molecules that form when sunlight breaks apart water vapor. This is a classic signature of cometary activity, indicating that 3I/ATLAS is shedding water as it warms near the Sun. Notably, no such signal was detected in September, suggesting that the comet’s activity increased as it approached the Sun, consistent with known cometary behavior. This detection strongly supports the conclusion that 3I/ATLAS is a water-rich, natural comet rather than an artificial object.
Despite these findings, the nature of 3I/ATLAS remains an open question, with the scientific community divided. On one side, the comet’s unusual resilience, powerful jets,