Discovery of 3I/ATLAS

On July 1, 2025, scientists using the ATLAS telescope in Chile announced the discovery of an extraordinary interstellar object named 3I/ATLAS, which has been tracked since June 14, 2025.

About 3I/ATLAS

1. Classification:

   • 3I/ATLAS is an interstellar comet, meaning it originates from outside our solar system.

   • Its highly elliptical orbit and fast velocity through space distinguish it from other solar system objects, making it a unique interstellar visitor.

2. Orbit and Speed:

   • The comet travels at speeds of 57–68 km/s relative to the Sun, much faster than objects within the solar system.

   • Its hyperbolic trajectory indicates it will pass through the solar system only once, without returning.

   • The comet's trajectory traces back to the constellation Sagittarius, indicating its origin lies far beyond our solar system, possibly from the Milky Way’s thick disk.

3. Key Dates:

   • Closest approach to Earth: About 270 million km.

   • Closest approach to the Sun: Expected on October 29–30, 2025, at a distance of around 210 million km, which is slightly within Mars’s orbit.

Physical Characteristics and Observations:

• Active Comet: 3I/ATLAS is confirmed to be an active comet, displaying a visible coma (a cloud of ice particles and dust) surrounding its nucleus.

• As it nears the Sun, it is expected to develop a tail, a characteristic feature of comets formed by the heating of the comet’s surface by the Sun.

• Reddish Hue: The comet has been observed to have a reddish hue, and its spectral characteristics suggest that its surface may be rich in complex organic compounds or water ice.

• Size: The nucleus of 3I/ATLAS is estimated to be 10–30 km wide, making it larger than previous interstellar visitors:

  • 1I/ʻOumuamua (2017): The first known interstellar object.

  • 2I/Borisov (2019): The second interstellar comet discovered.

• Composition and Rotation: The composition and rotation period of the comet are under active study using ground-based telescopes worldwide.

About Comets

1. Composition:

   • Comets are icy celestial bodies made up of frozen gases like water, ammonia, methane, and carbon dioxide, mixed with rocky and metallic dust.

2. Orbits:

   • Comets have highly elliptical orbits that take them far from the Sun and then close to it, unlike the near-circular orbits of planets.

   • Short-period comets originate from the Kuiper Belt, while long-period comets are thought to come from the distant Oort Cloud (located between 5,000–100,000 AU from the Sun).

3. Comet Features:

   • As comets approach the Sun, they heat up and release gases and dust, forming a coma (a cloud around the nucleus) and sometimes a tail.

   • One of the most famous comets, Halley’s Comet, visits Earth once every 76 years, with its last appearance in 1986.

Conclusion:

The discovery of 3I/ATLAS provides scientists with a rare opportunity to study a comet from outside our solar system, which could offer clues about the early solar system and the formation of celestial bodies.