NASA-funded ATLAS (Asteroid Terrestrial-impact Last Alert System) telescope in Rio Hurtado, Chile, first reported Comet 3I/ATLAS to the Minor Planet Center. Pre-discovery observations from ATLAS telescopes and Caltech’s Zwicky Transient Facility extend its visibility back to 14 June 2025.
Key Facts About 3I/ATLAS:
- It is third known interstellar object ever observed after: 1I/ʻOumuamua (2017) and 2I/Borisov (2019)
- Categorized as interstellar because of its hyperbolic orbit — not bound to the Sun, meaning it came from outside our solar system.
Trajectory and Proximity:
- Discovered Location: ~670 million km from the Sun (within Jupiter’s orbit).
- Closest Approach to Earth: ~1.8 AU (~270 million km or 170 million miles) — no threat to Earth.
- Closest Approach to Sun: ~1.4 AU (~210 million km) — near Mars orbit around 30 October 2025.
- Reappearance Post-Sun Passage: Early December 2025.
Naming Convention:
Comets are generally named for their discoverer(s), in this case the ATLAS survey team.
- 3I = Third Interstellar Object
- ATLAS = Named after the survey that discovered it
- “I” = Indicates interstellar origin (unbound to solar gravity)
Where Did It Come From?
- Formed in another star system, ejected into interstellar space, and has drifted for millions to billions of years.
- Entered solar system from the direction of the Sagittarius constellation — the center of the Milky Way galaxy.
Why It’s Interstellar:
- Follows a hyperbolic trajectory — moving too fast to be captured by Sun’s gravity.
- Will exit the solar system permanently after passing the Sun.
Nature and Composition:
- Exhibits activity: has a coma (gas/dust cloud) and likely an icy nucleus.
- Classified as a comet, not an asteroid, due to visible outgassing.
- Size: Not yet known.
- Speed:221,000 kmph or 61 km/s — will increase near the Sun.
Is It Dangerous
- No. Will not come closer than 1.6 AU (~240 million km or 150 million miles) to Earth.
- Poses zero collision threat
Significance:
- 3I/ATLAS provides a rare opportunity to study an interstellar visitor.
- Enhances understanding of cometary science, interstellar material, and formation of distant planetary systems.