December is a month of expectation for those who watch the sky: the interstellar comet 3I/ATLAS, which has become a curious phenomenon, is days away from passing its closest point to our planet, a date that, for scientists, represents the best opportunity to study planetary material originating from another star.
A visitor from outside our system
3I/ATLAS was unveiled in July 2025 when it was confirmed as the third object of its type in history, which already makes it exceptional. NASA determined that this comet travels at an impressive 220,470 kilometers per hour.
Its trajectory is what fascinates astronomers: it was ejected from its home star system and traveled billions of years from the constellation Sagittarius.
The key is its hyperbolic orbit, which means that the comet does not revolve around the Sun like ours, but will visit us only once before finally leaving our neighborhood and returning to interstellar space. It is estimated that its solid, icy nucleus could be between 1,400 feet and 3.5 miles wide.
What will happen on December 19 with the 3I/ATLAS
Perigee, or the comet’s closest approach to Earth, will be on December 19. Although the word “closest approach” sounds dramatic, the reality is that 3I/ATLAS will pass about
For amateur observers, patience and equipment are required:
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It is not visible to the naked eye. Due to its low luminosity, it requires the use of optical instruments, such as astronomical binoculars or a small telescope.
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Best time: The comet will be best appreciated during the pre-dawn hours, with the sky dark, looking towards the southeast horizon.
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Those who want to follow its path in real time can do so through NASA’s “Eyes on the Solar System” simulation.
Science versus fiction
The unusual nature of 3I/ATLAS has inevitably fueled theories beyond astronomy. The most widely circulated hypothesis was that of Harvard astrophysicist Avi Loeb, who raised the possibility that the object could be an “alien spacecraft” or some form of extraterrestrial technology.
Although Loeb himself admitted that it is most likely of natural origin, the space agencies have been firm in their denial. Nicola Fox, from NASA, has assured that the observations have been clear and that “we certainly have not seen any technosignatures or anything that would lead us to believe that this is anything other than a comet”: 3I/ATLAS is simply a comet from somewhere else.
