The comet 3I/ATLAS, recognized as the third confirmed interstellar object, is set to reach its perihelion on October 29, 2025, at a distance of 1.36 astronomical units from the Sun. This comet was initially discovered in July 2025 by the ATLAS telescope located in Chile. It travels along a hyperbolic orbit characterized by an eccentricity exceeding 5.
The impending close approach to the Sun subjects the comet”s nucleus to intense radiation, which may lead to the evaporation of volatile materials and potential fragmentation. Recent observations have indicated the presence of dust and ice jets directed toward the Sun, with images captured by the Nordic Optical Telescope between July and September 2025 showing extreme negative polarization.
The composition of 3I/ATLAS, rich in carbon dioxide and various metals, implies that it formed in a frigid environment, likely within another star system. Astronomers have noted a sudden increase in brightness, suggesting the ejection of material from within the comet. This extreme negative polarization distinguishes 3I/ATLAS from other known celestial bodies.
Data indicates that the comet may have originated from a region akin to the external Kuiper Belt. Currently, the comet is positioned behind the Sun from our perspective on Earth, although monitoring continues via coronagraph telescopes like CCOR-1 aboard the GOES-19 satellite. A Thai amateur astronomer managed to capture images of 3I/ATLAS on October 21, 2025, revealing a gas and dust coma despite significant solar glare.
After its perihelion passage, the comet will become visible during dawn in November, traversing through the constellations Virgo and Leo. NASA”s Europa Clipper mission is expected to intersect with the comet”s ion tail in late October, approximately 300 million kilometers from the Sun. Meanwhile, the European Space Agency”s Juice mission will approach within 64 million kilometers on November 4, utilizing instruments to perform multi-spectral composition measurements. These encounters aim to gather data on charged particles and verify the integrity of the nucleus following perihelion.
Ground-based telescopes are set to resume observations of 3I/ATLAS in November and December 2025, as the comet gradually moves away from the Sun. Notably, on November 3, it will come within 0.65 astronomical units of Venus. Sky survey networks are expected to detect any dust trails that may arise during this period.
For context, the comet 2I/Borisov fragmented in March 2020, following its perihelion in December 2019. Observations by the Hubble Space Telescope revealed that the nucleus split into two distinct pieces separated by a distance of 180 kilometers, occurring at a distance of 2 astronomical units from the Sun. Chemical analyses of the remnants indicated the presence of water and organic compounds similar to those found in local comets, a process that accelerated its rotation to the point of breaking apart. The release of dust from the comet enabled detailed chemical investigations.
Researchers are set to keep a close watch on 3I/ATLAS in March 2026, as it will cross the orbit of Jupiter at a distance of 54 million kilometers. The Juno probe will record any gravitational interactions during this time, further enhancing the monitoring efforts for hyperbolic objects. The relative speed of such interstellar visitors is typically around 60 kilometers per second, contributing to the expanding catalogs of documented passages.
