3I/ATLAS, the third recorded object that comes from outside, It will reach its closest point to the Sun, its perihelion, on October 29, 2025. This approach will be a decisive scientific window to try to answer the big question: is it simply a comet with exotic characteristics, or an artificial object with intriguing behavior?
According to orbital calculations, 3I/ATLAS will reach perihelion on October 29, 2025, at a distance of approximately 1.3564 AU (about 203–206 million km from the Sun). At that point, it will move at its maximum speed relative to the Sun. Days before perihelion, 3I/ATLAS will pass through solar conjunction: it will be practically behind the Sun from the Earth’s perspective, making it impossible to observe with conventional ground-based telescopes during that period.
That means that the direct observation window will be closed right at the key moment, limiting what we can see to instruments that do not depend on direct line of sight. Before approaching the Sun, 3I/ATLAS has already shown signs of outgassing, that is, the release of volatile gases (as is common in comets) even when it was ~6.4 AU from the Sun.
Recent images have suggested that its tail could be “growing” as it receives more solar heat. Furthermore, a color change towards green has been observed, indicating unconventional active chemical processes.
Scientists like Avi Loeb have proposed more speculative scenarios: that 3I/ATLAS could carry weak propulsion, or even be an artificial probe. The fact that the object is active even far from the Sun and that it shows unusual leaks has fueled such speculation.
SETI, for example, responded to these ideas by pointing out that, sIf the object accelerates, some would see it as artificial, but we lack conclusive evidence: It remains more plausible that it is a natural comet with extreme behavior.
Why is perihelion a unique opportunity? When approaching the Sun, the heat can activate the deeper volatile layers. New gases, abrupt changes in coma, or even a burst of activity that reveals what lies beneath its surface could be observed.
If the object shifts its trajectory with extra acceleration (beyond solar gravity), that could indicate internal “pushes,” i.e., anisotropic evaporation, directional gas release, or even artificial mechanisms. That is one of the keys to differentiating an astronomical object from a technological one.
Instruments such as the James Webb Space Telescope (JWST) They plan to observe the object before and after perihelion. Its infrared sensitivity can reveal molecules such as water, CO, CO₂ or ammonia that could provide clues to its origin.
Compare how the chemical activity changes, the morphology of coma, gas release rate, etc., before and after perihelion, is vital to construct a behavioral profile. If something “turns on” only at a certain distance range, that fuels “thermal activation” hypotheses.
The disadvantage: Being behind the Sun means that optical instruments from Earth cannot see its maximum activity. That gap can hide critical moments. It may depend on space telescopes or ships around Mars or to the other side of the Sun to capture it.
The visibility windows before and after perihelion are short and full of interference (sunshine, atmospheric disruptions). Emission rates can be weak, difficult to separate from the stellar background. Any Changing trajectory requires very precise measurements in position and speed. If the object suddenly “turns off” due to lack of volatiles, we could be left without signals just when we need them most.
That October 29 is not just any date: It is the moment when everything we know about 3I/ATLAS will be put to the test. If we observe unexpected accelerations, unusual emissions or new chemical species, radical dynamical behaviors… then we could get closer to the most fascinating answer of all: is it natural or is it something different?
And if the answer is that it is a natural object, that is also good news: It will confirm limits to what interesting objects can do and how much mystery remains in the unknown.