The interstellar comet 3I/ATLAS, discovered by the NASA-funded ATLAS telescope in Chile on July 1, 2025, approaches its closest point to the Sun on October 30, 2025, at 1.4 astronomical units. This third confirmed interstellar object passes through the solar system on a hyperbolic orbit, originating from outside its gravitational bounds.
Astronomers confirmed 3I/ATLAS as an interstellar visitor through analysis of its trajectory, which demonstrates it is not gravitationally bound to the Sun. Pre-discovery images captured by the Zwicky Transient Facility and three ATLAS telescopes located worldwide provided additional data to verify its path and entry into the solar system. These observations established the comet’s hyperbolic orbit, distinguishing it from solar system objects with elliptical paths. The discovery process involved coordination among international telescope networks, enabling rapid classification following the initial detection in Chile.
The comet’s orbital path brings it to perihelion, its closest solar approach, at approximately 1.4 astronomical units, equivalent to 130 million miles or 210 million kilometers. This position places it just inside the orbit of Mars. Throughout its passage, 3I/ATLAS maintains a minimum distance from Earth of 1.6 to 1.8 astronomical units, or about 150 to 170 million miles. Astronomers have calculated that this separation ensures no collision risk or threat to planetary bodies in the inner solar system.
Observations reveal unusual physical and chemical behaviors in 3I/ATLAS as it nears the Sun. Unlike typical comets, where material forms a tail pointing away from solar radiation pressure, this object exhibits jets of material directed toward the Sun. Instruments detect shifting chemical emissions and an unexplained acceleration in its motion. These anomalies, noted in data from the James Webb Space Telescope, Keck Observatory, and Hubble Space Telescope, deviate from standard cometary responses to solar heating. Scientists monitor these features to document changes in activity intensity and composition during the approach.
Such atypical behaviors challenge established models of comet physics, prompting detailed studies of how interstellar objects interact with solar radiation and gravitational influences. The James Webb Space Telescope provides spectroscopic analysis of the comet’s composition, while the Keck Observatory tracks surface changes, and Hubble captures high-resolution images of its structure. These combined efforts aim to catalog the object’s response to environmental factors unique to its interstellar origin.
Ground-based telescopes can track 3I/ATLAS through September 2025, after which its proximity to the Sun renders it unobservable during perihelion. The comet emerges from this period for renewed observations in early December 2025, allowing continued monitoring as it departs the inner solar system. This visibility window supports global astronomical campaigns to gather data on its evolution.
As the third confirmed interstellar object, following 1I/ʻOumuamua and 2I/Borisov, 3I/ATLAS presents an opportunity to examine materials and conditions from beyond the solar system. Researchers analyze its surface ices, dust particles, and volatile compounds to understand formation processes in distant stellar environments. This direct sample of extraterrestrial matter informs models of planetary system development elsewhere in the galaxy.
The comet’s discovery has generated public interest, including speculation from Harvard professor Avi Loeb that it might represent an alien spacecraft. NASA has addressed these claims by affirming that 3I/ATLAS constitutes a natural cometary body, based on orbital and compositional evidence from telescopic observations.
