When it comes to space oddities, everyone seems to be glued to one object at the moment: Comet 3I/ATLAS. The mysterious comet, with its blue-green glow and dusty tail, has raised an endless stream of questions since its initial discovery in July 2025.
Astronomers and amateur space enthusiasts alike have been pondering over the original home of this visitor to our solar system; some people have even capitalized on the excitement over Comet 3I/ATLAS to interject with narratives that it could be related to extraterrestrial life.
The long and short of it is that there isn’t any evidence that points to Comet 3I/ATLAS being a spaceship piloted by aliens, a far-fetched theory that scientists have been trying to shut down. But what is the true identity of Comet 3I/ATLAS? Find out what scientists have already uncovered about the interstellar object, from its origins to its chemistry.
Read More: When Was Halley’s Comet Last Seen and Will It Ever Return?
A Visitor to Our Solar System
NASA’s Swift Ultraviolet/Optical Telescope (UVOT) observed interstellar comet 3I/ATLAS during two visits in July and August 2025. The panels show visible-light (left) and ultraviolet (right) images, where the faint glow of hydroxyl (OH) traces water vapor escaping from the comet. Each image combines dozens of short, three-minute exposures, painstakingly stacked to reach total integration times of about 42 minutes in visible light and 2.3 hours in ultraviolet. Swift’s vantage point above Earth’s atmosphere allowed astronomers to detect these ultraviolet emissions that are normally invisible from the ground.
(Image Credit: Dennis Bodewits, Auburn University)
On July 1, 2025, the Asteroid Terrestrial-impact Last Alert System (ATLAS) survey telescope in Chile caught a glimpse of something entering the inner solar system at speeds of 137,000 MPH. This was the very first sighting of Comet 3I/ATLAS.
The hyperbolic shape of the comet’s orbital path confirmed that it’s not gravitationally bound to the sun, meaning it will pass right through the solar system before continuing its journey across deep space. This also led scientists to declare that Comet 3I/ATLAS is only the third interstellar object ever recorded, hence the “3I” in its name (“I” standing for interstellar).
On October 30, 2025, the comet reached its perihelion, or its closest approach to the sun, at 210 million kilometers.
A Colorful Cloud and Tail
Like other comets, Comet 3I/ATLAS has a core made of solid ice and a bright cloak of gas and dust that has been fashioned into a long tail. Its icy nucleus is estimated to be anywhere from 3.5 miles (5.6 kilometers) to 1,000 feet (320 meters) in diameter, although scientists are working to get a better idea of its true size, according to a study in The Astrophysical Journal Letters.
The gas and dust that surrounds it, forming into a cloud called a “coma,” has been seen growing as it approaches the sun. This is a normal occurrence for other comets that pass the sun; as they get closer to the star’s blazing heat, the frozen gases on their surface sublimate, meaning they transition from a physical to a gaseous state without melting into a liquid.
Comet 3I/ATLAS’s blue-green tail has been growing as well; this is due to solar wind blowing its coma back, causing gas and dust to trail behind it.
There are a few additional aspects of Comet 3I/ATLAS that make it stand out from other comets. The most obvious is that it comes from some unknown origin beyond our solar system. Only two other objects with interstellar origins have been observed: 1I/’Oumuamua in 2017 and 2I/Borisov in 2019.
Comet 3I/ATLAS, however, has taken a different path than the previous two interstellar objects. Its trajectory appears to be far steeper and faster, and it also indicates that the comet may have originated from the Milky Way’s “thick disk” — a collection of stars that orbit above and below the thin plane where the sun resides.
Since it formed outside of our solar system, Comet 3I/ATLAS may be the oldest comet ever seen, according to a study in the Royal Astronomical Society. While non-interstellar comets can be up to 4.5 billion years old, Comet 3I/ATLAS may be a few billion years older.
Why Comet3I/Atlas Is Important
Astronomers have also taken note of the comet’s composition — its coma is emitting an unusually high amount of carbon dioxide gas, but it also contains carbon monoxide (CO). They’ve also found water on the comet through its ultraviolet byproduct, hydroxyl (OH), which can absorb radiation. The comet’s water content may hint at how interstellar comets form and how the building blocks of life take shape beyond the solar system.
Recently, a radio telescope operated by the South African Radio Astronomy Observatory detected a radio signal from the comet based on radio absorption by hydroxyl radicals. This establishes that, without a doubt, Comet 3I/ATLAS is a natural comet, and nothing else.
The comet will make its closest approach to Earth on December 19, 2025 at 270 million kilometers from our planet, according to the European Space Agency. But rest assured, we aren’t in any danger. The comet will later fly past Jupiter in March 2026 and eventually leave the solar system to continue its journey. Until then, astronomers will look closely at Comet 3I/ATLAS in hopes of finding out what other clues it may hold about deep space.
Read More: Could Alien Life Travel on Interstellar Asteroids and Comets like ‘Oumuamua?
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