3I/ATLAS
Interstellar comet · 2025 N1
3I/ATLAS became the third recognised interstellar object after ATLAS reported it in July 2025. Its hyperbolic orbit carried it past the Sun in October 2025 and back towards interstellar space. Webb observations investigated unusual isotope ratios and tiny grains containing water ice mixed with dust. Studies reported in 2026 use those measurements to constrain cold formation conditions and material processing, while the nucleus’s exact history remains model-dependent.
Understand this world
What does 3I/ATLAS reveal about comets from other stars?3I/ATLAS became the third recognised interstellar object in 2025. Follow how its orbit, isotope measurements and Webb’s ice-grain spectra test its formation history. · 3 minMeasurements
- Effective diameter
- Not available
- Semimajor axis
- -0.264 AU
- Orbital period
- Not available
Orbit, physical values and uncertainties
- eccentricity
- 6.123467394525528 ± 4.3958E-5
- semi-major axis
- -.2638835217034532 au ± 1.7786E-6
- perihelion distance
- 1.351998619400212 au ± 4.0631E-6
- inclination; angle with respect to x-y ecliptic plane
- 175.2403121571192 deg ± 7.6824E-5
- longitude of the ascending node
- 323.0251782090054 deg ± .00052433
- argument of perihelion
- 128.7969426041922 deg ± .00052907
- mean anomaly
- 2636.10924225336 deg ± .025326
- time of perihelion passage
- 2460977.941795880909 TDB ± .0001844
- sidereal orbital period
- Not available
- mean motion
- 7.270858064454297 deg/d ± 7.3509E-5
- aphelion distance
- Not available
- comet total magnitude
- 11.8 ± 01.
- comet total magnitude slope
- 7.5
Published JPL orbital elements describe their stated epoch; they are not current positions. Small-body diameters can be effective/model-dependent sizes, not spherical shapes. Missing measurements remain unavailable. Pluto’s diameter uses the New Horizons reference rather than an empty SBDB field. Orbital epoch: JD 2461340.5 TDB.
Object reference ↗Missions & milestones
0 launches · 0 connected events
These are target-related flights and every connected programme record in the production catalogue. A connected event may concern another stage or target of the same journey. Launch outcome does not establish arrival or current operation.
No verified target-related flight is linked in the production catalogue.
Complete source cohort: 9,390 records.