The interstellar comet 3I/ATLAS made its closest approach to the sun on October 29 and 30, as observed from Earth. This event offered a unique opportunity to study material originating from outside our solar system. Discovered on July 1, 2025, by the Asteroid Terrestrial-impact Last Alert System telescope in Chile, 3I/ATLAS is the third recognized interstellar object to traverse our solar system, following 1I/Oumuamua in 2017 and 2I/Borisov in 2019.
On October 21, the comet reached solar conjunction, positioning itself on the opposite side of the sun from Earth, which temporarily hindered ground-based observations. It is anticipated to reach perihelion at approximately 1.4 astronomical units, or 210 million kilometers, from the sun, placing it just within the orbit of Mars.
NASA”s assets, including the Hubble Space Telescope and the James Webb Space Telescope, along with spacecraft operating near Mars, have been monitoring the comet”s trajectory. Observations from Hubble suggest that the diameter of the comet”s nucleus ranges between 440 meters and 5.6 kilometers.
Dr. Bryce Bolin, the lead author of a study on the comet, remarked, “It”s like an aeon-old fridge, which will open during the next months to release some of its contents.” The comet is classified as an active object, featuring a solid icy nucleus accompanied by a coma, which is a cloud of gas and frozen dust that escapes from the nucleus. Spectroscopic studies have identified water ice, carbon dioxide, cyanide, and nickel in the comet”s coma.
Fortunately, the comet poses no danger to Earth, as it will pass at a distance of approximately 270 million kilometers during its closest approach on December 19. Following this, it is expected to come within 54 million kilometers of Jupiter on March 16, 2026, before continuing its journey into interstellar space.
Recent observations from the Southern African Large Telescope in Sutherland, South Africa, have indicated that the comet has a rotational period of 16.16 hours and shows increasing dust activity. The months of November and December will provide optimal conditions for observation as the comet emerges from behind the sun, likely becoming brighter following its perihelion passage. It is expected to reach a magnitude of 10 in early November, making it visible through telescopes, although not to the naked eye.
Research suggests that the age of the comet could range between 3 and 14 billion years, potentially predating our solar system, which is about 4.6 billion years old. Scientists believe that 3I/ATLAS may have been ejected from its parent star system due to a close encounter with a large planet or another nearby star.
