The interstellar comet 3I/ATLAS, the third confirmed object from outside our solar system, approaches its closest point to the Sun on October 30, 2025. This perihelion will occur at about 1.4 astronomical units (AU), or roughly 130 million miles (210 million kilometers), just inside Mars’ orbit. Discovered on July 1, 2025, by the NASA-funded Asteroid Terrestrial-impact Last Alert System (ATLAS) telescope in Chile, the comet’s path was confirmed through pre-discovery images from the Zwicky Transient Facility and three ATLAS telescopes around the world.
Unlike objects bound to the Sun, 3I/ATLAS follows a hyperbolic orbit, indicating its interstellar origin. It joins 1I/ʻOumuamua, detected in 2017, and 2I/Borisov, found in 2019, as the only other confirmed visitors from beyond our solar system. The comet poses no risk to Earth, maintaining a distance of 1.6 to 1.8 AU, or about 150 to 170 million miles, from the planet throughout its passage.
Astronomers have noted unusual behavior as 3I/ATLAS nears the Sun. Instead of a tail pointing away from solar radiation, the comet exhibits material jets directed toward the Sun. Observations reveal shifting chemical emissions and unexplained acceleration, captured by instruments on the James Webb Space Telescope, Keck Observatory, and Hubble Space Telescope. These features deviate from typical cometary activity and prompt scientists to revisit existing models of comet physics.
Ground-based telescopes can track the comet until September 2025. Around perihelion, its proximity to the Sun will make observation difficult, but it should become visible again in early December 2025. This trajectory provides a limited window for detailed study of its composition and dynamics.
The comet’s interstellar nature allows researchers to examine materials and conditions from another star system. Data from 3I/ATLAS could yield insights into the formation and evolution of distant planetary systems. The discovery has generated public interest, including speculation from Harvard professor Avi Loeb that it might represent an alien spacecraft. NASA has stated that the object is a natural cometary body, based on current observations.
Teams continue to monitor 3I/ATLAS for further developments in its activity and trajectory. The event underscores the role of survey telescopes like ATLAS in detecting rare solar system intruders.
