An interstellar comet that sparked speculation about extraterrestrial visitors has departed the solar system after making its closest approach to Earth at 270 million kilometres on December 19, with Russian scientists dismissing claims the object could be an alien spacecraft, RIA Novosti reported on December 24.

The object designated 3I/ATLAS was discovered on July 1, 2025, by a Chilean telescope operated by NASA's Asteroid Terrestrial-impact Last Alert System. Its high velocity, exceeding 50 kilometres per second, and unusual trajectory identified it as interstellar.

Harvard University astronomer Abi Loeb published an article suggesting the cosmic object could have technological origins with a crew inside, claiming aliens might be hostile and planning to approach Earth covertly from the direction of the Sun. "The consequences could be catastrophic for humanity," Loeb stated in his blog, provoking media sensation.

Natan Eismont, lead researcher at Russia's Space Research Institute, stated nothing surprising occurred in the comet's behaviour.

"Of course it has peculiarities, such as increased carbon dioxide content. Otherwise there are no miracles, everything within known physics. Changes in velocity can be related to gas and dust emissions, which is typical for comets," Eismont stated.

The researcher noted that controversy raised by Loeb proved beneficial by attracting public attention to science and potentially increasing funding for planetary defence programmes. Observation capabilities are growing, raising chances of detecting genuinely dangerous objects in time, Eismont stated. "I think Loeb understands perfectly well that everything he says is fiction," the researcher noted.

Loeb's article, published on a preprint site, contains an important caveat describing the work as "primarily a pedagogical exercise".

The comet's coma measures approximately 24 kilometres in diameter. Its trajectory suggested it arrived from the thick disc of the Milky Way galaxy, estimated at seven billion years old, rather than the younger thin disc containing the 4.5 bn-year-old solar system.

NASA scientists believe the object could have originated in an ancient planetary system predating our own.

3I/ATLAS became the third known visitor from another star system in eight years. The Pan-STARRS telescope detected cigar-shaped asteroid 1I/Oumuamua in 2017, whilst Crimean amateur astronomer Gennady Borisov spotted the first interstellar comet 2I/Borisov in 2019.

Eismont stated such discoveries will increase in coming years as telescope capabilities improve sharply. Interstellar objects visited the solar system previously but could not be registered, whilst visits from other galaxies are possible though far rarer.