Astronomers Discover Third Interstellar Object 3I/ATLAS

Context: On July 1, scientists operating the ATLAS telescope in Chile announced the discovery of a celestial object named 3I/ATLAS, which had been under observation since June 14.

About 3I/ATLAS Interstellar Object

• 3I/ATLAS is an interstellar comet, possibly the oldest comet ever observed, potentially older than the solar system by over 3 billion years.
• It was identified based on its highly elliptical, hyperbolic orbit and high velocity of 57–68 km/s relative to the Sun.
• Its path points back to the constellation Sagittarius, indicating an origin outside the solar system, possibly from the Milky Way’s thick disk.
• Because of its hyperbolic orbit, it will pass through the solar system once only and never return.

Closest Approaches

• Closest approach to Earth: ~270 million km
• Closest approach to the Sun: ~210 million km, expected on October 29–30, 2025, just inside Mars’s orbit.

Physical Characteristics

• 3I/ATLAS is an active comet, displaying a coma — a cloud of dust and ice particles around its nucleus.
• It is expected to form a tail as it nears the Sun due to solar heating.
• Photometric studies reveal a reddish colour, with a spectral slope of ~1.3% per 100 nm, indicating the presence of complex organic molecules or water ice.
• The nucleus is estimated to be 10–30 km wide, making it larger than previous interstellar visitors:
  • 1I/ʻOumuamua (2017)
  • 2I/Borisov (2019)

Ongoing Research

• Its composition and rotation period are currently under active investigation using ground-based telescopes across the globe.

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