Astronomers have reported that the interstellar object 3I/ATLAS is exhibiting unexpected acceleration as it traverses the Solar System. Recent measurements indicate a slight but notable acceleration that does not fit neatly within conventional comet behavior models. This finding, initially noted by NASA engineers and subsequently examined by international research teams, has piqued interest and caution within the astronomy community.
Some scientists argue that the acceleration can be attributed to natural processes such as outgassing, while others suggest that further investigation is required to ascertain the cause of this motion. Among those exploring this phenomenon is Avi Loeb, an astrophysicist at Harvard. He contends that while a natural explanation is the most plausible, the existing data does not exclude the possibility of a technological source, such as an internal propulsion system.
A recent study co-authored by Loeb and his team analyzed over 4,000 ground-based observations of 3I/ATLAS collected between May and September 2025. The researchers established an upper limit on any non-gravitational acceleration, estimated at around 3 × 10−10 astronomical units per day squared. This suggests that if the object were indeed expelling gas or dust, typical of comets, it would need to be exceptionally massive or losing material in such a manner that produces negligible detectable thrust.
Based on these findings, scientists estimate that 3I/ATLAS has a minimum mass of approximately 3.3 × 10^16 grams and a diameter of at least five kilometers, which is notably large for an interstellar object. This limited yet intriguing acceleration is the foundation for Loeb”s more speculative interpretations. On his research blog, he remarked that the observed residual acceleration does not eliminate the possibility of propulsion. If 3I/ATLAS is as substantial as the estimates suggest, even moderate thrust from gas release or an internal mechanism may be too subtle for current detection methods.
Loeb proposed that during perihelion—the point at which the object comes closest to the Sun—there might be opportunities for a craft to alter its speed or orientation. He also speculated that smaller fragments could be released or that excess heat might point towards an internal energy source. However, he clarified that he does not assert that 3I/ATLAS is an extraterrestrial probe but emphasizes the importance of maintaining an open scientific perspective until definitive evidence is obtained.
Many in the scientific community prefer a more conservative interpretation of the data. Observations have revealed that 3I/ATLAS exhibits typical cometary characteristics, including a dust coma, variations in its tail when near the Sun, and traces of volatile gases like carbon dioxide. These features lead some researchers to argue for a natural origin. Critics also note that the presented acceleration is an upper bound rather than a confirmed measurement, and the object”s considerable mass could obscure any minor propulsive effects.
Organizations such as NASA and the European Space Agency continue to categorize 3I/ATLAS as a natural interstellar comet undergoing standard outgassing processes. The object is expected to make its closest approach to Earth in December, providing telescopes another opportunity to assess whether its trajectory continues to deviate from predictions. Future observations may reveal whether this anomaly stems from physical phenomena or something more extraordinary.
