The interstellar comet 3I/ATLAS passed through our solar system, becoming only the third such visitor ever recorded. Scientists tracked its journey past the Sun with telescopes around the world.
Every so often, an object arrives in our solar system from far beyond it, carrying clues about distant star systems. In 2025 astronomers identified one such visitor, an interstellar comet given the name 3I/ATLAS, and tracked it closely.
In this article we summarize what has been reported about 3I/ATLAS, from its discovery to its closest passes and the observations made along the way. The information is based on published details from NASA, ESA and observatories.
A Visitor From Another Star
According to NASA, 3I/ATLAS is a comet that is not gravitationally bound to our Sun, meaning it came from beyond our solar system. Objects like this pass through once and then continue on their way back into interstellar space.
Discovered From Chile
The comet was discovered by the NASA funded ATLAS survey telescope in Rio Hurtado, Chile, and reported to the Minor Planet Center on July 1, 2025. Its unusual path quickly marked it as something out of the ordinary for astronomers.
Only the Third of Its Kind
NASA notes that 3I/ATLAS is only the third known interstellar object ever observed passing through our solar system. It follows 1I/Oumuamua, seen in 2017, and the comet 2I/Borisov, which was observed in 2019.
Closest Pass by the Sun
According to NASA, 3I/ATLAS came closest to the Sun on October 30, 2025, at a distance of about 130 million miles, or roughly 1.4 astronomical units. At that point it was moving through the inner solar system at high speed.
A Safe Distance From Earth
NASA reported that on December 19, 2025, the comet was about 1.8 astronomical units from Earth, which is around 170 million miles. There was no danger to our planet, as the comet came no closer than that distance.
Observed From Around the World
The passage of 3I/ATLAS drew the attention of observatories on the ground and telescopes in space. Astronomers used the rare opportunity to gather as much data as possible while the visitor was within reach of their instruments.
Seen in X-ray Light
According to reports, X-ray space telescopes observed the comet in late 2025 and detected a diffuse X-ray glow around it. This made 3I/ATLAS the first interstellar comet to have been observed in X-ray light, a notable milestone.
Clues to Its Composition
Observations with radio and other telescopes reported the detection of gases around the comet, including molecules such as hydrogen cyanide, methanol and carbon monoxide. Such measurements help scientists understand what the object is made of.
A Look Past Mars and Jupiter
The comet also passed relatively close to Mars, where spacecraft orbiting the planet were able to observe it. Reports indicate that it later continued toward the outer solar system, making a distant pass by Jupiter in early 2026.
Why Interstellar Objects Matter
Interstellar visitors are valuable because they offer a rare chance to study material formed around other stars. By examining their composition and behavior, researchers can compare them with comets and asteroids from our own solar system.
A Fleeting Chance to Study
Because interstellar objects do not return, each one offers only a brief window for study before it leaves for good. The observations of 3I/ATLAS add to a small but growing record of visitors from beyond our solar system.
Solid take on NASA.
Well said.
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