A new telescope built to to track fast-moving space objects caught a comet from beyond the solar system moving across the sky — before anyone even knew it was there.
The NSF-DOE Vera C. Rubin Observatory in Chile recently captured rare footage of the visitor known as 3I/ATLAS — only the third interstellar object discovered. What’s more impressive: The observatory recorded the video a full 10 days before the comet was officially identified by NASA's Asteroid Terrestrial-impact Last Alert System.
Unlike the thousands of comets that loop around the sun, this one isn’t from around here. Scientists say 3I/ATLAS was born in a completely different star system and likely got flung into the void by the gravity of a nearby planet or passing star. After drifting for perhaps hundreds of millions of years, the giant comet, which you can watch in Rubin's video below, wandered into our realm — and it's just passing through.
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Comets are icy, rocky objects that travel through space, often trailing long, bright tails of gas and dust as they warm up near the sun. Scientists have detected over 4,000 of them so far, but many more awaiting discovery could be lurking beyond Neptune in the Kuiper Belt or even in the remote Oort Cloud, the outer edge of the solar system about 50 times farther away.
Unlike Halley’s Comet and others that regularly circle the sun, 3I/ATLAS isn’t one of the locals. When it was first spotted on July 1 by the ATLAS survey telescope, it was over 400 million miles from Earth and well within the orbit of Jupiter. At the time, it was traveling at a blistering speed of about 137,000 mph. That’s far too fast to be held by the sun’s gravity, confirming that it's on a one-way route through the solar system.
Experts say it's only the third-known interstellar comet. The first, a rocky cigar-shaped thing named 'Oumuamua, zoomed by in 2017. Then came 2I/Borisov in 2019, which looked and behaved a little more like a typical comet. Now, 3I/ATLAS joins this rare club, but scientists think it may be the most ancient of all.
Based on early computer models, researchers believe 3I/ATLAS may have come from a little-known region of the Milky Way filled with old, long-lived stars. If so, it could be over 7 billion years old — nearly twice as old as our own solar system. That makes it a sort of time capsule, preserving materials from an earlier time in the galaxy.
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Because it’s already releasing gas and dust as it heats up, astronomers know it’s made of ice — the hallmark of a comet — despite recent sensational headlines suggesting the object might be an alien spacecraft. Its dusty tail may become visible from Earth with a backyard telescope later this year or early in 2026.
"While there's nothing wrong with thinking about whether some interstellar objects could be alien technology," said Jason Wright, a Penn State astronomy and astrophysics professor, on X, "3I/ATLAS has had its coma clearly detected since July 3. It's very clearly, unambiguously, a comet."
Scientists are especially excited about this discovery not just because of what it is, but because of how it was found. The Rubin Observatory, while still being tested, managed to catch the comet before anyone even knew to look. That bodes well for the future. Researchers estimate Rubin could find dozens more of these interlopers in the coming decade — possibly up to 50.
Interstellar objects like 3I/ATLAS offer a direct glimpse into the chemical makeup of other planetary systems. Since they formed around different stars, studying them could reveal how worlds form in other parts of the galaxy — and whether the building blocks for life travel between stars.
Right now, 3I/ATLAS is about 262 million miles from Earth. It's expected to make its closest approach to the sun in late October, then swing back out, never to return. But no need to worry: This comet will stay far from Earth, never coming closer than about 150 million miles, but leaving behind a wealth of data for astronomers to study for years to come.
