Astronomers Study Rare Interstellar Visitor: Comet 3I/ATLAS

In a rare celestial event, Comet 3I/ATLAS, the third known interstellar object to traverse our solar system, is providing astronomers with an unprecedented opportunity to study material from beyond our cosmic neighborhood. Discovered on July 1, 2025, by the Asteroid Terrestrial-impact Last Alert System (ATLAS) in Rio Hurtado, Chile, this comet's journey offers valuable insights into the composition and behavior of interstellar bodies.

Comet 3I/ATLAS was identified when it was approximately 4.5 astronomical units (AU) from the Sun. Its hyperbolic trajectory and high velocity—initially about 137,000 miles per hour (221,000 kilometers per hour), increasing to approximately 153,000 miles per hour (246,000 kilometers per hour) at perihelion—confirmed its origin from outside our solar system. The comet's nucleus is estimated to be between 440 meters and 5.6 kilometers in diameter.

The comet reached its closest approach to the Sun on October 29, 2025, at a distance of 1.36 AU (203 million kilometers). It then passed within 0.65 AU (97 million kilometers) of Venus on November 3, 2025. The upcoming closest approach to Earth is projected for December 19, 2025, at a distance of about 1.8 AU (269 million kilometers), posing no threat to our planet.

Observations have revealed increased activity as 3I/ATLAS nears the Sun. Jets of gas and dust have been observed erupting from its surface, a phenomenon akin to cryovolcanism. These eruptions suggest internal heating and sublimation of ice, particularly solid carbon dioxide. Such activity places 3I/ATLAS in surprising similarity to trans-Neptunian objects—icy bodies that orbit our Sun beyond Neptune—even though the comet originated from an entirely different star system.

The Hubble Space Telescope captured detailed images of the comet's nucleus and surrounding coma on November 30, 2025, revealing faint signs of its tail and jet activity. Additionally, the European Space Agency's Jupiter Icy Moons Explorer (Juice) spacecraft, while en route to Jupiter, observed 3I/ATLAS, capturing images of its plasma and dust tails. Full scientific data from Juice is expected by February 2026.

NASA's Solar Terrestrial Relations Observatory (STEREO-A) also observed the comet between September 11 and 25, 2025, marking the first time NASA's heliophysics missions have knowingly observed an interstellar object. These observations contribute to a growing body of data that enhances our understanding of such rare visitors.

The passage of 3I/ATLAS through our solar system provides a unique opportunity to study the composition and behavior of interstellar objects, offering insights into the materials and conditions present in other star systems. Such studies can enhance our understanding of the formation and evolution of planetary systems beyond our own.

3I/ATLAS is the third known interstellar object to visit our solar system, following 1I/ʻOumuamua in 2017 and 2I/Borisov in 2019. Each of these discoveries has progressively expanded our understanding of interstellar objects and their diversity.

As 3I/ATLAS continues its journey through our solar system, astronomers worldwide remain vigilant, eager to glean as much information as possible from this rare interstellar visitor before it departs back into the depths of space.