3I/ATLAS

3I/ATLAS – An Ancient Interstellar Comet in the Solar System

Why in news: 

On July 1, 2025, astronomers using the ATLAS survey telescope in Chile discovered a new interstellar object, named 3I/ATLAS. It is only the third confirmed interstellar object observed in our solar system after 1I/ʻOumuamua (2017) and 2I/Borisov (2019).

Key Scientific Highlights:

1. Interstellar Nature Confirmed

• Highly elliptical and hyperbolic orbit, indicating it is not gravitationally bound to the sun.

• Speed: Traveling at approximately 57–68 km/s relative to the sun.

• Trajectory traced back to the constellation Sagittarius, suggesting origin from outside the solar system.

2. Timeline of Movement

• Closest approach to Earth: ~270 million km (no threat).

• Closest approach to the Sun: October 29–30, 2025, at ~210 million km, just inside Mars’s orbit.

• Will eventually exit the solar system permanently after perihelion.

3. Physical and Chemical Characteristics

• Identified as an active comet with a visible coma (cloud of dust and ice).

• May develop a tail as it nears the sun.

• Photometric analysis shows a reddish hue and a spectral slope of 1.3% per 100 nm, indicating:

  • Presence of complex organic molecules

  • Abundant water ice on the surface

• Estimated size of nucleus: 10–30 km — larger than both 1I/ʻOumuamua and 2I/Borisov.

• Composition and rotation are under global investigation using ground-based telescopes.

4. Possible Oldest Observed Comet

• Likely predates the solar system by over 3 billion years.

• May have originated in the Milky Way’s thick disk or from a long-dead star system in the galactic thin disk.

• Offers a rare opportunity to study primordial material from another star system.

Scientific and Astronomical Importance

• Could provide crucial insights into early galactic and planetary formation processes.

• Offers an opportunity to understand the building blocks of planets and organic chemistry in alien environments.

• Potential to study star system evolution, composition of interstellar objects, and extrasolar material.

International Collaboration and Monitoring

• Global observatories are actively monitoring the object’s:

  • Composition

  • Activity

  • Orbital dynamics

• Visibility: May be observable by amateur astronomers with small telescopes by late 2025 to early 2026.

The discovery of 3I/ATLAS marks a major milestone in interstellar research. As the oldest known interstellar comet, it opens a new chapter in understanding the cosmic origins of matter, organic compounds, and planetary formation, offering rare insights before it vanishes from view forever.