Comet 3I/ATLAS: Oldest Comet Visitor from Solar System?

Comet 3I/ATLAS, also known as C/2025 N1 (ATLAS), is an interstellar comet that made headlines after its discovery in July 2025. Scientists believe it could be at least 7 billion years old. Comet 3I ATLAS could be older than the solar system itself, if it originated from the Milky Way’s thick disk. 

Comet 3I/ATLAS is the third confirmed interstellar object ever detected, following ‘Oumuamua and 2I/Borisov. Learn about Comet 3I/ATLAS, its origins, discovery, why it is turning green and visibility in December 2025.

Is Comet 3I/ATLAS the Oldest Comet Visitor from the Solar System?

Comet 3I/ATLAS could be at least 7 billion years old, older than the solar system, if it originated from the thick disk of the Milky Way. Its trajectory of this interstellar comet is unbound and hyperbolic, confirming its interstellar origin.

Scientists have collected 122 observations from 31 observatories to confirm its path and age. Comet 3I/ATLAS’s potential age makes it a unique visitor, offering clues about the early universe and the composition of interstellar objects.

When was Comet 3I/ATLAS Discovered?

Comet 3I/ATLAS was first spotted on July 1, 2025, by the NASA-funded ATLAS survey telescope in Río Hurtado, Chile. Pre-discovery observations extend back to June 14, 2025, using data from multiple ATLAS telescopes and the Zwicky Transient Facility.

Check Out | List of 9 Comets NASA Is Tracking, #3 Is an Interstellar Visitor

Why is Comet 3I ATLAS Turning Green?

Comet 3I/ATLAS is turning green because of diatomic carbon (C2) molecules in its coma, which glow green when sunlight hits them. As the comet heats up near the Sun, these molecules get excited and emit green light. This is a common comet feature, but the shift from red to green shows new gases are being released as the comet warms up. The green color gives scientists clues about the comet’s chemistry and how it’s changing as it travels through space.

Will Comet 3I/ATLAS be Visible in December 2025?

By December 2025, Comet 3I/ATLAS will be moving away from the Sun and will again be visible to telescopes on Earth. The James Webb Space Telescope (JWST) is scheduled to observe the comet in December 2025, after its perihelion.

Read | NFL Christmas Games 2025: Date, Teams, Schedule & Where to Watch?

Conclusion

Comet 3I/ATLAS stands out as a remarkable interstellar visitor, possibly the oldest comet ever observed. Its discovery in July 2025 and ongoing visibility through December 2025 offer a rare opportunity to study material from beyond our solar system, deepening our understanding of cosmic history.