A giant comet spotted days ago hurtling through the solar system may be the most ancient one ever seen — and may be loaded with frozen water.
The icy traveler, called 3I/ATLAS or Comet ATLAS, was discovered on July 1 by the NASA-funded ATLAS survey telescope in Río Hurtado, Chile. This enormous space snowball came from the direction of the constellation Sagittarius and is about 300 million miles from Earth right now.
After running a new kind of computer simulation, scientists believe the comet originated from a rarely seen corner of the galaxy, far beyond the birthplace of the sun. And because it likely formed around an ancient, thick-disk star in the Milky Way, it should be rich in water ice, said Matthew Hopkins, a University of Oxford astronomer, who led the research. If early predictions bear out, this object may be over 7 billion years old — born more than 3 billion years before this solar system existed.
Every planet, moon, asteroid, and life form orbiting the sun shares a common heritage, built from the same materials about 4.6 billion years ago. But interstellar visitors are true outsiders.
"They are remnants of other planetary systems, carrying with them clues about the formation of worlds far beyond our own," the European Space Agency said. "These icy wanderers offer a rare, tangible connection to the broader galaxy — to materials formed in environments entirely unlike our own."
Comets are balls of ice, dust, and rock, known for their telltale tails — millions-of-miles-long debris trails of vaporizing material. More than 4,000 comets are known, but astronomers say countless others are likely orbiting the sun beyond Neptune in a disk known as the Kuiper Belt or on the outer edge of the solar system, in the so-called Oort Cloud, about 50 times farther from the sun.
Unlike Halley’s Comet and others that regularly circle the sun, Comet ATLAS isn’t one of the locals. It’s only the third object ever confirmed to have come from far beyond the solar system. And this one might be the most significant. Astronomers say it’s on a steep, unusual path that hints it formed near ancient stars orbiting in a thicker region of the Milky Way — an area scientists know less about.
"This is an object from a part of the galaxy we’ve never seen up close before," said Chris Lintott, a co-author on the new findings, which Hopkins presented at the Royal Astronomical Society's National Astronomy Meeting on Friday.
The researchers' computer simulation, dubbed the Ōtautahi–Oxford Model, marks the first real-time application of predictive modeling to an interstellar comet. It was created to estimate how many such interstellar objects the new Vera C. Rubin Observatory might find, relying on information about their orbits and likely stellar origins.
The discovery offers a rare chance to study a frozen fragment from the galaxy’s early days, the researchers say. If the comet formed around one of those older stars, it would help confirm that ice-rich materials were free-floating between star systems long before the sun entered the universe — and may still be delivering materials to young planetary systems today.
Based on the study, the team believes there's a two-thirds chance the comet is older than our own solar system, and that it’s been drifting through space ever since.
Comet ATLAS has already started waking up from its hibernation. As it moves closer to the sun, its surface heats up, releasing gas and dust. Early glimpses with some of the world's largest telescopes suggest it may even be larger than the other two known interstellar visitors: 'Oumuamua, which swung by in 2017, and Borisov, which came and went two years later.
If their predictions are confirmed, this could have implications for how many similar objects Rubin will likely detect. It may also provide clues about the role interstellar comets play in seeding new worlds across the galaxy. Researchers believe the powerful telescope in Chile could uncover dozens more such visitors — maybe even up to 50 over the next decade.
Comet ATLAS poses no threat to Earth and will remain at a distance of 150 million miles, even at its closest approach to the sun around Oct. 30. Stargazers might get a shot at seeing the comet for themselves with a backyard telescope this fall or in early 2026 after it reappears on the other side of the sun.
