Interstellar Comet 3I/ATLAS: What Scientists Know About the Third Visitor From Beyond

An unusual visitor from beyond our solar system continues to capture the attention of astronomers around the world. The interstellar comet known as 3I/ATLAS remains a focus of study, offering scientists a rare chance to examine an object that formed around another star far from our own.

A visitor from beyond the solar system

According to NASA, 3I/ATLAS was discovered by the NASA-funded ATLAS survey telescope located in Rio Hurtado, Chile, and was reported to the Minor Planet Center on July 1, 2025. It stands as only the third interstellar object ever observed passing through our solar system.

The name itself explains its significance. The number three indicates that it is the third such object detected, while the letter I stands for interstellar, confirming that the comet originated somewhere beyond the boundaries of our own solar system before crossing our path.

Its journey around the Sun

NASA reports that the comet reached its perihelion, the closest point to the Sun, on October 30, 2025. At that moment it was about 1.4 astronomical units from the Sun, a distance equal to roughly 210 million kilometers, or around 130 million miles from our star.

The object is also remarkably fast. At the time of its discovery it was traveling at about 137,000 miles per hour, and by the time it reached perihelion its speed had increased to roughly 153,000 miles per hour, according to the space agency's measurements.

The size of its nucleus

Estimating the size of the comet has been part of the scientific effort. NASA notes that the diameter of the nucleus of 3I/ATLAS is thought to be no smaller than about 440 meters and no larger than roughly 5.6 kilometers, leaving a wide range still to be refined by observation.

No danger to Earth

Despite its passage through the inner solar system, the comet posed no threat to our planet. According to NASA, 3I/ATLAS came no closer than about 1.8 astronomical units to Earth, a distance of roughly 270 million kilometers, or about 170 million miles away from us.

Still under observation

Even after its closest approach to the Sun, the comet remains an object of interest for telescopes. According to sky-tracking resources, in this period 3I/ATLAS lies in the direction of the constellation Gemini, where astronomers can continue to follow its path across the sky.

New research after perihelion

Recent research carried out after perihelion has added to the picture. Studies published in September 2026 report that the unusual polarimetric properties of 3I/ATLAS have persisted across perihelion and match independent observations made during the same period by other teams.

Polarimetry is a technique that studies how light is polarized when it interacts with the dust and material surrounding a comet. By measuring these properties, scientists can gather clues about the nature of the particles that make up the object and how it behaves over time.

The findings suggest that there has been no significant evolution in the polarimetric properties of the comet across its passage near the Sun. That consistency gives researchers a clearer baseline as they compare 3I/ATLAS with comets that originate within our own solar system.

Why interstellar objects matter

Interstellar objects like 3I/ATLAS are extremely rare, which is why each detection draws intense scientific interest. As only the third confirmed visitor of its kind, the comet offers a direct opportunity to study material that formed in a completely different planetary system.

What comes next

As the comet continues its journey outward, astronomers are expected to keep observing it for as long as it remains within reach of their telescopes. Each new measurement adds to the growing record of a rare guest that briefly passed through our corner of the galaxy.