Interstellar object
A small body — asteroid, comet, or otherwise — that originates outside our solar system and passes through it on a hyperbolic trajectory. As of 2026, three confirmed interstellar objects have been detected: 1I/'Oumuamua (2017), 2I/Borisov (2019), and 3I/Atlas (2025–2026).
An interstellar object is a small body — typically an asteroid or comet — that originates outside our solar system and passes through it on a hyperbolic trajectory (one with eccentricity greater than 1, meaning the object is not gravitationally bound to the Sun). Such objects are visible from Earth for only a brief period as they transit the inner solar system.
Confirmed interstellar objects (as of 2026)
Three interstellar objects have been formally designated by the International Astronomical Union:
- 1I/’Oumuamua (October 2017) — discovered by the Pan-STARRS survey in Hawaii. The first confirmed interstellar object. Notable for its unusual elongated shape, lack of detected cometary activity, and small but significant non-gravitational acceleration that became a subject of substantial scientific discussion.
- 2I/Borisov (August 2019) — discovered by amateur Ukrainian astronomer Gennady Borisov. Behaved as a normal comet from an interstellar origin, with detectable gas and dust outgassing.
- 3I/Atlas (2025–2026) — the third confirmed interstellar object, currently in the inner solar system and the subject of ongoing observation. Its anomalous brightening event of 21–23 April 2026 is documented in the Council’s archive as Case #00482.
Why they matter
Interstellar objects are scientifically valuable because they are physical samples of other solar systems — material that formed elsewhere and is now passing through our neighborhood. Spectroscopy of such objects provides direct information about the chemistry and conditions of distant star systems.
They are also occasionally invoked in UAP discourse as a framework for considering whether some observed objects might be artificial probes (see the bracewell-probe glossary entry) rather than natural bodies. To date, no observed interstellar object has produced evidence requiring an artificial interpretation; ‘Oumuamua’s anomalies were the most-cited but are accounted for by natural-comet hypotheses with appropriate model adjustments.
Detection rate
The discovery of three interstellar objects in less than a decade — when none had been confirmed in the entire prior history of astronomy — reflects the substantial improvement in modern survey telescopes (Pan-STARRS, ATLAS, the Vera Rubin Observatory). Some estimates project that the Vera Rubin Observatory’s Legacy Survey of Space and Time (LSST), beginning operations in 2025, will detect interstellar objects at rates of one or more per year.
Council position
The Council treats interstellar objects as astronomical phenomena governed by standard scientific epistemology. We track them in our archive when they exhibit anomalous features (as 3I/Atlas has done) and update our verdict as observational data accumulates. Speculation about artificial origin is identified as such and is held to a standard of evidence not yet met by any observed interstellar object.