1I/'Oumuamua
1I/'Oumuamua is the first confirmed interstellar object — a small body that entered the Solar System from beyond it, rounded the Sun in September 2017, and is now departing on a one-way hyperbolic path it will never retrace. It was observable for only about two weeks and has not been seen since, so its position is CALCULATED, not tracked: as of August 2026 it is roughly 54 AU from the Sun (well beyond Neptune) and receding toward the constellation Pegasus. It was never resolved, so almost everything about it carries real uncertainty.
Key facts
Science
Physical
- Dimensions
- 0.48 × 0.16 × 0.16 km · approx. triaxial diameter
- Rotation period
- 7.94 hours
Composition
- Make-up
- A dry, reddened surface resembling organic-rich or space-weathered material seen on some outer-Solar-System bodies. No coma, dust or gas tail was ever detected, so it was classed as asteroidal — yet a small non-gravitational acceleration was measured as it left, hinting at faint outgassing (or another mechanism). Its make-up is inferred from colour and motion, never sampled.
Radiation & temperature
- Insolation
- 0.000342 S⊕ · 1/2,925 of the sunlight Earth receives
Discovery & history
Discovered on 19 October 2017 by Robert Weryk with the Pan-STARRS1 telescope on Haleakala, Hawaii, days after it had already rounded the Sun. Its strongly hyperbolic orbit (eccentricity ~1.2) showed immediately that it came from beyond the Solar System — the first such visitor confirmed, which is why it carries the '1I' interstellar designation. It was named 'Oumuamua, Hawaiian for a scout or messenger reaching out from the distant past. A small non-gravitational acceleration was measured as it departed; whether from faint outgassing or another cause is still debated. It was observable for only about two weeks; no spacecraft visited it, and it will never return.
Images
Images from open archives · credit shown per image