Interstellar comet 3I/ATLAS: third known visitor from beyond Solar System
Why in the news
Astronomers are studying 3I/ATLAS, the third interstellar object ever confirmed. It arrives from beyond the Solar System on a hyperbolic path and may be among the oldest comets observed.
Key facts
- Discovered on 1 July 2025 by the NASA-funded ATLAS survey station at Rio Hurtado in Chile.
- Designation: C/2025 N1 (ATLAS); it comes from the direction of Sagittarius.
- Speed estimated at 57-68 km/s along a hyperbolic orbit, which shows its interstellar origin.
- Shows an active coma, water ice and complex organic compounds.
- Closest approach to the Sun on 29 October 2025 at 1.36 AU.
Interstellar objects so far
| Object | Year |
|---|---|
| 1I/ʻOumuamua | 2017 |
| 2I/Borisov | 2019 |
| 3I/ATLAS | 2025 |
About its origin
It likely comes from the thick disk of the Milky Way. Models suggest a 70% probability that it is more than 3 billion years older than the Solar System, and it may be over 7 billion years old. It is moving faster than the two earlier interstellar visitors. Its closest approach to Earth is expected in December 2025, at roughly 1.8 AU.
Exam angle
- The “I” in 3I stands for interstellar; the number gives the order of detection.
- Discovery year 2025 and the ATLAS survey are the usual facts.