Understanding Interstellar Objects
Visitors from beyond the Solar System — what makes an object interstellar, how hyperbolic orbits reveal it, how the confirmed objects (1I/ʻOumuamua, 2I/Borisov, 3I/ATLAS) were found, and how astronomers tell them apart from Solar-System comets and from unconfirmed candidates. Built on real MPC/JPL data; confirmed and candidate objects are kept clearly separate and nothing is fabricated.
- 1.1What is an interstellar object?A body from another star system, passing once through our own.
- 1.2Hyperbolic orbitsUnbound trajectories that never return — and where they come from.
- 1.3Eccentricity greater than oneWhy an eccentricity well above 1, with excess speed, means interstellar.
- 1.4How interstellar objects are detectedThe excess-velocity signature that betrays a visitor from another star.
- 2.11I/ʻOumuamuaThe first interstellar object — elongated, dry, and much-discussed.
- 2.22I/BorisovThe first clearly cometary interstellar object, rich in carbon monoxide.
- 2.3Comets vs asteroids vs interstellar objectsTelling a visitor from another star from a hyperbolic Solar-System comet.
- 2.4Survey telescopesPan-STARRS, ATLAS, and Catalina — the wide-field surveys that catch them.
- 3.1The Minor Planet CenterOrbit determination and the IAU “I” interstellar designations.
- 3.2Candidate and debated objectsThe CNEOS 2014 bolide and why some interstellar claims stay disputed.
- 3.3What interstellar objects revealSpectroscopy of material formed around other stars.
- 3.4Future interstellar surveysWhy the Vera C. Rubin Observatory should find many more.
Related entities
- Interstellar object
1I/ʻOumuamua
The first confirmed interstellar object, detected in October 2017 on its way out of the Solar System. Its strongly hyperbolic orbit (eccentricity about 1.2) showed it was never bound to the Sun. It displayed no visible coma, is highly elongated, and showed a slight non-gravitational acceleration — features that drew wide attention, though the scientific consensus is that it is a natural body.
- Interstellar object
2I/Borisov
The second confirmed interstellar object and the first that was unmistakably a comet, discovered in August 2019 by amateur astronomer Gennadiy Borisov. Its eccentricity of about 3.4 made its interstellar origin certain. Unlike 1I/ʻOumuamua it showed an active dust coma and tail, letting astronomers study the chemistry of a comet formed around another star; it proved unusually rich in carbon monoxide.
- Trajectory class
Interstellar Hyperbolic Trajectory
A strongly hyperbolic trajectory — eccentricity well above 1 with a large excess velocity relative to the Sun — that cannot be produced by planetary perturbations. This is the signature of an interstellar object: a body that entered the Solar System already unbound, from another star system, and will leave on the same path. 1I/ʻOumuamua, 2I/Borisov, and 3I/ATLAS all follow such trajectories.
- Detection method
Excess Hyperbolic Velocity
The primary signature of an interstellar object: its speed relative to the Sun exceeds the local escape velocity by enough that the orbit is strongly hyperbolic (eccentricity well above 1). A large hyperbolic excess velocity (v∞) cannot be produced by planetary perturbations, so it points to an origin outside the Solar System. A small excess, by contrast, can come from a planetary slingshot and does not by itself prove an interstellar origin.