3I/ATLAS captured by the Gemini North telescope. Image credit: International Gemini Observatory/NOIRLab/NSF/AURA/K. Meech (IfA/U. Hawaii); Image Processing: Jen Miller & Mahdi Zamani (NSF NOIRLab)
Dr. Avi Loeb of Harvard suggests there is a 30-40% likelihood that the interstellar object 3I/ATLAS is artificial, in short, an alien spacecraft. Drawing on seven peculiarities, Loeb claims the object does not seem to have natural origins and has been scheduled to fly past the Earth from late November through December of 2025.
The peculiarities include: its enormous size of greater than 5 km, its unique chemical composition of more nickel than iron, its extremely negative light polarization not previously observed in comets, that it aligned with both the ecliptic plane of our solar system and the 1977 Wow! signal, and its recent flybys of Mars, Venus, and Jupiter that all exhibited extremely precise sail-like trajectories.
SETI responded with a detailed rebuttal, based on work by Dr. Eahsanul Haque, which showed that the properties observed would still best be explained by rare, but perhaps possible, natural astrophysical processes. According to Haque, this object likely originated from the galactic thin disk, where alignments with the ecliptic plane are much more likely to arise statistically.
Regardless of the origins, we can confidently say that 3I/ATLAS is one of the most mysterious visitors to the solar system and warrants consideration from both the conventional and unconventional domains.
References:
https://eartharxiv.org/repository/view/9820
https://www.theguardian.com/science/2025/sep/11/interstellar-comet-nasa-alien-made