How do we know 3I/ATLAS is from another star system? The orbit of 3I/ATLAS. (Image credit: NASA/JPL-Caltech) What makes astronomers certain about the interstellar nature of 3I/ATLAS is its trajectory.

3I/ATLAS streaks across a dense star field in this image captured by the Gemini North telescope's Gemini Multi-Object Spectrograph (GMOS-N). The image is composed of exposures taken through three ...

More information: Darryl Z. Seligman et al, Discovery and Preliminary Characterization of a Third Interstellar Object: 3I/ATLAS, arXiv (2025). DOI: 10.48550/arxiv.2507.02757 ...

Matthew J. Hopkins et al, From a Different Star: 3I/ATLAS in the context of the Ōtautahi-Oxford interstellar object population model, arXiv (2025). DOI: 10.48550/arxiv.2507.05318 , ...

3I/ATLAS is estimated to be, at most, about 20 kilometers in size. It is currently located about 670 million kilometers from the sun and is approaching our star from the direction of Sagittarius ...