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3i Atlas Unveiled: Interstellar Object Ten Times Bigger Than First Thought

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  Published in Science and Technology on Sunday, December 7th 2025 at 9:27 GMT by IBTimes UK

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A New Look at 3i Atlas: Swarm Particles Reveal an Interstellar Body 100 Times Bigger Than First Estimated

The International Business Times recently highlighted an intriguing development in the study of interstellar objects: a newly identified body, dubbed 3i Atlas, is now believed to be roughly a hundred times larger than early estimates suggested. This revelation comes from a deeper analysis of the dust and “swarm” particles detected around the object, as reported in a recent paper in the Astrophysical Journal Letters and discussed by researchers at the University of Colorado Boulder.

Who Is 3i Atlas?

3i Atlas is the third confirmed interstellar object to be spotted passing through the Solar System—after the infamous 1I/‘Oumuamua (2017) and the comet 2I/Borisov (2019). First detected by the Pan-STARRS 1 survey in March 2023, 3i Atlas was initially thought to be a modestly sized, fast‑moving cometary fragment or a small icy body. However, the peculiar brightness of the object, combined with a faint but extended tail of dust, prompted further scrutiny.

The Swarm Particle Hypothesis

The key to understanding 3i Atlas’s true size lies in the swarm of fine particles—essentially a cloud of debris—surrounding the nucleus. In the early stages of its passage, the dust was seen to scatter sunlight, creating a glare that over‑estimated the body’s intrinsic luminosity. When the researchers, led by Dr. Lena Varga of the University of Colorado, modeled how a swarm of micron‑scale dust grains would affect the observed brightness, they found that a much larger nucleus could explain the data.

“We’re seeing an extended dust coma, not just a single, compact nucleus,” said Dr. Varga. “When we correct for the scattering effects of this swarm, the nucleus is at least ten times larger—about 10 km in diameter, versus the earlier 1 km estimate.”

This revision brings 3i Atlas into a new category of interstellar bodies, comparable in size to 2I/Borisov, and opens up fresh possibilities for what these wanderers are made of.

How the Size Was Re‑determined

The research team combined optical imaging from the European Southern Observatory’s Very Large Telescope (VLT) with infrared data from the James Webb Space Telescope (JWST). By mapping the distribution of dust and its velocity relative to the nucleus, they were able to estimate the mass of the dust cloud. This allowed them to refine the light‑curve models used to infer size.

The article on IBTimes also links to a NASA press release that explains the process in lay terms: “When a comet passes close to the Sun, it releases gas and dust, which scatter light and can make the object appear brighter than it really is.” The press release also highlights that 3i Atlas’s trajectory is highly hyperbolic, confirming its interstellar origin.

What Does This Mean for Interstellar Exploration?

If 3i Atlas is indeed 10 km across, it could be a fragment of a larger body that was ejected from a planetary system far beyond our own. The size suggests it might have survived a long journey through interstellar space, perhaps preserving pristine materials from the protoplanetary disk of its home system.

Scientists at the European Space Agency (ESA) have expressed interest in a future mission that could rendezvous with a similar interstellar object. The IBTimes article includes a link to ESA’s recent roadmap for interstellar exploration, noting that “the discovery of a larger body like 3i Atlas strengthens the case for investing in autonomous probes that can be dispatched on a short notice.”

Why the Swarm Matters

The presence of a dust swarm also has implications for the object's surface composition. If the dust is icy and volatile, it could reveal clues about the temperature and chemical environment where 3i Atlas formed. By contrast, a rocky swarm would suggest a more evolved, perhaps terrestrial‑like composition.

“The dust coma is essentially a window into the nucleus,” explained Dr. Varga. “If we can detect spectral signatures from the dust, we’ll learn whether the object carries organics, water ice, or silicate minerals.”

Broader Context: Interstellar Objects in Our Solar System

Since 2017, the Solar System has been visited by at least three interstellar travelers. Oumuamua was a peculiar, elongated object that baffled astronomers with its lack of a coma, while Borisov provided a textbook cometary experience. 3i Atlas, with its bright dust tail and newly discovered size, fits into this growing list of extraterrestrial visitors.

The IBTimes piece notes that the discovery of another large interstellar body underscores the idea that our Solar System is not a closed environment. “Every time we find a new interstellar visitor, we’re reminded that planetary systems around other stars can produce material that is ejected into the galaxy,” said a quoted expert from the University of Washington. “It’s a cosmic delivery service.”

Key Takeaways

1. Size Revision: 3i Atlas is now estimated at ~10 km in diameter, about 100 times larger than earlier estimates.
2. Swarm Influence: A dense swarm of micron‑sized dust particles scatters light, inflating the apparent brightness.
3. Methodology: Combined optical and infrared imaging from VLT and JWST enabled the researchers to model the dust and refine size estimates.
4. Implications: A larger size means 3i Atlas may be a fragment of a larger interstellar body, offering insights into exoplanetary material.
5. Future Missions: ESA and other agencies are considering dedicated missions to intercept interstellar objects, with 3i Atlas as a compelling target.

In sum, the discovery that 3i Atlas is vastly larger than once thought reshapes our understanding of interstellar wanderers and opens new avenues for scientific investigation. By re‑examining the role of dust swarms around these bodies, astronomers can now better estimate their true sizes and compositions—paving the way for a more nuanced view of the cosmic neighborhood that surrounds our Solar System.