James Webb Telescope CONFIRMS 3I/ATLAS Is Much Bigger Than We Thought

[00:00:00]On the 25th of August 2025, NASA released a single image that quietly rewrote what astronomers thought they knew about the object now known as threeey atlas. The picture came from the James Webb Space Telescope. And it showed something no human eye had ever captured before. The chemical fingerprint of a comet that was born before our sun existed, traveling through the solar system on a path that will take it away from us forever. What Webb found inside that fingerprint was strange enough to make veteran astronomers pause. The object was releasing gas at a rate that should have measurably altered its trajectory. And yet, it wasn't budging. It was radiating carbon dioxide in proportions almost never seen in a comet. And buried in the glow of its own dust cloud was a solid core that turned out to be far larger, far older, and far heavier than anyone expected when it was first spotted a month earlier. This is the story of how that discovery unfolded, what it means, and why the more we look at three Atlas, the stranger it becomes. The story begins on the 1st of July, 2025 at an observatory in Chile that most people outside of astronomy have never heard of. The Asteroid Terrestrial Impact Last Alert System, known by its acronym, Atlas, is a network of telescopes built for one specific purpose, to scan the sky every single night and catch anything that might be on a collision course with Earth. It is not designed to hunt for cosmic mysteries. It is designed to buy humanity warning time if a rock the size of a building happens to be heading our way. But on that July night, the systems software flagged something unusual. A faint point of light was moving across the frame in a way that didn't match anything orbiting our sun. Objects bound to the solar system trace ellipses, curved paths that loop around and eventually return. This object was tracing a hyperola, an open curve that comes in once and never comes back. Within hours, astronomers around the world had confirmed it. This was only the third object ever detected that had definitively originated. Outside our solar system, a visitor from another star entirely. It was given the designation three atlas, the number three marking it as the third interstellar object ever cataloged following the strange elongated visitor called Umuamua in 2017 and the comet Borisov in 2019. What made three Atlas different from the moment of its discovery was its size and its speed.

[00:02:11]Early calculations showed it moving at roughly 137,000 mph relative to the sun.

[00:02:17]a velocity so extreme that no force in our solar system could have produced it.

[00:02:21]Only an origin beyond our own stars gravity could explain that kind of speed. And unlike Umwamua, which was small, dark, and gone before most telescopes could get a good look, threeey atlas was bright enough and would remain visible long enough for scientists to actually study it in detail. This was, in other words, the first real chance humanity had ever had to closely examine a piece of another solar system as it passed through our own. Astronomers moved quickly. Within 3 weeks of discovery, the Hubble Space Telescope was retasked to observe the object, capturing its first images on the 21st of July. What Hubble saw was captivating. The comet was surrounded by a teardrop-shaped cocoon of dust, a glowing envelope called a coma streaming away from a solid nucleus buried somewhere at its center. Because Hubble was tracking the comet's motion during the long exposure, the background stars appeared as streaks of light while the comet itself sat crisp and defined in the frame. It was visually one of the most striking images ever taken of an interstellar object. But it was also frustrating in a very specific way. The coma was so bright and so effective at scattering sunlight that it completely obscured the solid body underneath.

[00:03:30]Astronomers could see that something was there generating all of this activity, but they could not yet measure it directly. What they could do was estimate an upper and lower boundary based on how much light the object was reflecting and how that light behaved.

[00:03:42]Those first Hubble based calculations released in early August suggested the nucleus could be anywhere from about 440 m across, roughly the length of four football fields end to end, up to as large as 5.6 km, more than 3 mi wide.

[00:03:57]That is an enormous range of uncertainty, roughly a factor of 12 between the smallest and largest possible size. For scale, an object at the small end would still be a substantial minor body. But one at the large end would rank among the biggest comets ever observed passing through our solar system dwarfing most short and long period comets that scientists have cataloged from within our own stellar neighborhood. The honest answer at that point was that nobody knew. The dust was in the way and dust does not care about scientific curiosity. This is where the James Webb Space Telescope enters the story and where the real transformation in our understanding began. Web was built for exactly this kind of problem.

[00:04:34]Its instruments are tuned to infrared light, wavelengths invisible to the human eye, but exceptionally good at piercing through dust and revealing the chemical composition of whatever that dust is made of. On the 6th of August 2025, WEB turned its near infrared spectrograph, an instrument known as NIspec, toward threei atlas. The results were announced by NASA on the 25th of August, and they immediately reframed the conversation around this object.

[00:04:58]What Webb detected was a coma dominated overwhelmingly by carbon dioxide. In most comets that originate within our own solar system, water ice is the primary driver of activity. As a comet approaches the sun and warms up, the ice sublimates, turning directly from solid to gas. And that outgassing is what creates the glowing coma and the long trailing tail that makes comet so visually distinctive. But 3II Atlas was different. Web's spectroscopic data showed a ratio of carbon dioxide to water that was measured at roughly 7.6 to1, a proportion so far outside the normal range for comets that researchers described it as among the highest ever recorded. Statistically speaking, this measurement sat more than four standard deviations away from the typical trend line that astronomers use to describe how comets behave at this kind of distance from the sun, excluding only one previously known outlier comet with an unusual chemical history. In simpler terms, if you lined up every comet ever measured and plotted their chemical ratios on a graph, three eye atlas would sit far outside the cluster where nearly everything else falls. Alongside the carbon dioxide, Web also picked up signatures of water, carbon monoxide, water ice itself, fine dust particles, and a tentative, not yet confirmed trace of a compound called carbonyl sulfide.

[00:06:12]Later, spectroscopy conducted from the ground using the very large telescope in Chile added another layer, confirming the presence of cyanide gas and detecting nickel within the coma, elements that had previously only been observed together in a small number of unusual solar system comets. The presence of nickel is worth sitting with for a moment because it says something deeper about how this object was built.

[00:06:33]Nickel is a metal and finding it vaporized into gas form in a comet's coma at such a great distance from the sun is not something researchers expected to see so clearly. It suggests that whatever process assembled three eyed atlas billions of years ago incorporated metallic material directly into its icy structure in a way that allows it to be released as the comet warms even at relatively low temperatures. This kind of chemistry gives scientists clues not just about what the object is made of but about the environment in which it originally formed information that is otherwise completely inaccessible to us because we cannot travel to another star system and study its planet forming disc directly.

[00:07:12]Three Atlas is in a very real sense bringing a sample of that distant environment to us. Then in December of 2025 after the comet had swung around the sun and begun its outbound journey back toward interstellar space, Webb observed it again. This time using a different instrument called MIRI, the mid- infrared instrument. The second observation added a genuinely new piece to the puzzle. Buried in the mid infrared spectrum at a wavelength of about 7.6 micrometers, Web's team detected a clear signature of methane.

[00:07:41]This was significant for a very specific reason. It was the first time methane had ever been confirmed in any interstellar object. Methane is a molecule that tends to be extremely volatile, meaning it sublimates and escapes into space at very low temperatures. Its survival inside the nucleus of threeey atlas in a form stable enough to be detected billions of years after the comet formed tells researchers something important about how cold and how undisturbed the object's interior has remained since its birth. Alongside the methane, the December observation reconfirmed water, carbon dioxide, and the atomic nickel signature first hinted at earlier in the year, painting an increasingly detailed and increasingly unusual chemical portrait. Now, back to the question of size, because this is where the story your headline is chasing really comes into focus. For months after discovery, the size of three eye atlas's solid nucleus remained frustratingly uncertain, trapped behind that wide range Hubble had first established, somewhere between 440 m and 5.6 6 km.

[00:08:39]The problem again was the coma. Dust and gas streaming off the nucleus reflect and scatter sunlight in ways that make the underlying solid body almost impossible to isolate using visible light alone. But by combining data across multiple instruments and multiple observing sessions, using Hubble's high resolution imaging alongside web's infrared spectroscopy and thermal modeling of how the object absorbs and remits heat, researchers were finally able to narrow that uncertainty down dramatically. The updated analysis places the solid core of 3i Atlas at approximately 2.6 km across. A figure that sits solidly within the upper half of the original estimated range and one that carries far more confidence behind it than the earlier back of envelope calculations. 2.6 km might not sound enormous when you first hear the number roughly 1 and a half miles across, but context matters enormously here. And the context is what makes this genuinely remarkable. Um, MUA, the first interstellar object ever detected back in 2017, was estimated to be perhaps a few hundred meters at most along its longest axis and by some models potentially even smaller. Boris, the second interstellar visitor detected in 2019 had a nucleus estimated at under a kilometer, likely somewhere around 4 to 500. Dread meters. Compared to both of its predecessors, 3II Simeia Atlas is not just somewhat bigger. Researchers studying its mass now estimate that it is tens of times more massive than Umuamua and Borisov combined. This is not a subtle difference. This is an object that fundamentally changes the size distribution we thought we understood for interstellar visitors.

[00:10:13]And it raises a genuinely important question that astronomers are still working through. Is 3i Atlas simply an unusually large outlier, a rare giant among what should mostly be small fragments? Or does its size tell us that interstellar space is full of objects like this and that we have simply lacked the observational tools until very recently to detect them reliably? The mass of the object connects to another strange thread in this story, one that has generated real scientific debate.

[00:10:40]Harvard astrophysicist Avi Lobe, who has built a career studying interstellar objects and has been a vocal, sometimes controversial, voice in the public conversation around three Atlas, published an analysis using the web data from early August. His team calculated that the comet was losing mass through outgassing at a rate of roughly 150 kg every second with the escaping gas traveling at speeds of around 440 m/s.

[00:11:05]Under the basic physics of momentum conservation, a process every rocket engineer understands intuitively. That kind of outgassing should produce a measurable non-gravitational push on the object, subtly bending its trajectory away from the path a purely gravitational orbit would predict.

[00:11:21]Comets do this all the time. It is one of the ways astronomers routinely refined their understanding of a comet's mass and structure. But when Loe's team looked for that expected deviation in three eye atlas's path, they didn't find it, or at least not to the degree the outgassing rate should have produced.

[00:11:37]The conclusion drawn from this absence is that the object must be considerably more massive than its outgassing alone would suggest. Massive enough that the escaping gas simply isn't strong enough relative to the object's own gravity and inertia to meaningfully shift its course. It's worth being clear that this finding along with some of Loe's broader conclusions about the object's population statistics remains a subject of debate within the astronomical community and not every researcher studying three Atlas agrees with every interpretation he has proposed. Science works this way. A surprising measurement gets published, other teams try to replicate it, challenge it, or refine it and the truth gets sharpened through that friction over time. It's also worth addressing directly the speculation that inevitably follows any object this strange. the question of whether threeey atlas could be artificial, some kind of probe or spacecraft rather than a natural comet. This idea gained traction online almost as soon as the object was discovered, fueled in part by Umuam Mua's own history of speculation back in 2017 when its unusual elongated shape and lack of a visible tail led some researchers, including Loe himself, to publicly float the possibility that it might not be a natural object at all.

[00:12:44]With three Atlas, the same kind of speculation resurfaced almost immediately. But the overwhelming consensus among astronomers actually studying the data is that ThreeI Atlas is behaving exactly like a comet should.

[00:12:55]It has a visible coma. It is actively outgassing volatile compounds in response to solar heating exactly as ice bodies do when they warm up. Its chemical composition dominated by carbon dioxide, water, carbon monoxide, and now methane matches the kind of ices you would expect to find in a body that formed in a cold, distant region of a planet forming disc around another star.

[00:13:15]None of this rules out curiosity or careful scrutiny. And scientists are right to examine every anomaly closely, including the mass discrepancy lobe identified. But examining an anomaly carefully is very different from concluding it must be artificial. Every piece of hard spectroscopic and imaging evidence gathered so far points toward a natural, if unusually large, and unusually old comet. And that brings us to perhaps the most staggering figure to come out of the entire investigation.

[00:13:41]the age of three US Atlas. Using models built from the comet's orbital dynamics, its trajectory through the galaxy, and the chemistry web detected in its coma, researchers have estimated that this object formed somewhere between 10 and 12 billion years ago in a cold distant region of the early Milky Way galaxy. To put that in perspective, our own sun and solar system are approximately 4.6 billion years old. Uh that means threeey atlas could be more than twice as old as Earth itself. And at the upper end of that range, its formation would sit not far behind the estimated age of the Milky Way galaxy and the universe as a whole, which is roughly 13.6 billion years old. This is an object whose ice began forming when the universe was in its adolescence. Long before our sun ignited, long before the Earth accreted from a disc of dust and rock, long before life of any kind existed anywhere we know of, it has been drifting through interstellar space, essentially frozen and unchanged for the vast majority of the universe's entire history, only to drift by pure chance through our particular corner of the galaxy at exactly the moment humanity had built telescopes sensitive enough to notice it. Researchers studying this finding, including scientists outside the original team who have reviewed the preprint, have emphasized what this really means scientifically. A researcher at the Royal Belgian Institute for Space Aronomy, who was not involved in the original study, but reviewed its findings, noted that this evidence points to three eye atlas having formed in a stellar environment fundamentally different from our own, not simply in a different location in space, but during a dramatically earlier chapter in the Milky Ways history. It is worth being transparent that this age estimate, like several of the more striking claims about 3II Atlas, comes from research that is still working through peer review, posted on pre-print servers before formal publication and independent verification. That doesn't mean the finding is wrong. It means it is provisional, part of the normal, sometimes messy process by which science refineses extraordinary claims before they become accepted fact. Extraordinary claims of this kind, an object potentially twothirds the age of the universe itself, deserve exactly that kind of careful skeptical scrutiny before they're treated as settled.

[00:15:48]Before we reach that conclusion, it is worth stepping back into the observatories themselves because the way this data was gathered is almost as remarkable as what it revealed. Web was never originally scheduled to spend its limited, highly competitive observing time on a newly discovered comet. Every hour of that telescope's time is allocated years in advance through a rigorous proposal process. Astronomers around the world compete fiercely for even a few minutes of its attention because it is by a wide margin the most powerful infrared observatory ever built. But space agencies maintain a small reserve of discretionary time specifically for events like this genuine scientific emergencies where a rare timelmited opportunity appears with no warning.

[00:16:28]Three hour atlas qualified instantly within roughly 5 weeks of its discovery.

[00:16:32]Telescope schedulers had cleared time.

[00:16:35]Engineers had recalibrated pointing coordinates, and Web's mirrors, sitting nearly a million miles from Earth, at a gravitationally stable point called the second Lrangee point, swung toward a target that did not exist in anyone's observing plan a month earlier. That kind of rapid response is itself a demonstration of how seriously the scientific community treats interstellar visitors precisely because they are so rare and so fleeting. Once an object like this passes beyond the reach of our instruments, the opportunity to study it directly closes permanently, and there is no way to know how many years or decades might pass before another one arrives. Close enough and bright enough to examine this closely again. The instruments themselves deserve a moment of explanation because understanding how they work makes the findings feel less like abstract numbers and more like genuine detective work. Web's near infrared spectrograph doesn't simply take a picture. It splits incoming light into its component wavelengths.

[00:17:27]essentially building an extraordinarily detailed rainbow out of the faint glow coming from the comet's coma. Every chemical compound absorbs and emits light at very specific well doumented wavelengths. Fingerprints as unique and as reliable as the ridges on a human hand. When Web's spectrograph recorded a spike in brightness at the precise wavelength associated with carbon dioxide and a much smaller spike at the wavelength associated with water, that wasn't a guess or an inference. It was a direct chemical readout gathered from roughly 270 million miles away of gas molecules escaping a frozen body that had been drifting through the void since before our galaxy looked anything like it does today. The mid- infrared instrument used in the follow-up December observations works on a similar principle, but is tuned to slightly longer wavelengths, which is precisely why it was able to catch the methane signature that the August observations using a different wavelength range had missed entirely. Combining both instruments gave researchers a far more complete chemical picture than either could have produced alone. And it illustrates why multiple observations spread out over months and using different tools matter so much in this kind of research. A single snapshot can mislead. A layered repeated investigation cross-cheed across instruments is what actually builds scientific confidence. The size measurement followed a similarly layered process, and understanding it helps explain why earlier estimates were so uncertain and why the newer figure carries so much more weight. Astronomers cannot simply point a telescope at a comet's nucleus and read off a diameter the way you might measure a table with a tape measure. Instead, they rely on a technique that combines how much sunlight the object reflects, called its albdo, with how much heat it absorbs and radiates, measured through infrared observations. A small, highly reflective object and a large, dark, less reflective object can sometimes produce similar amounts of visible brightness, which is exactly why the earliest Hubble-based estimates spanned such a wide range. Because visible light alone could not distinguish between those possibilities, web's infrared thermal data broke that ambiguity. By measuring the object's actual heat signature rather than relying solely on reflected sunlight, researchers could calculate a far more reliable estimate of the nucleus's true surface area and from there its diameter. This is the same fundamental technique astronomers use to measure the size of asteroids throughout our own solar system. And applying it to an object passing through from another star system entirely represents a genuine milestone in observational astronomy. proof that the tools built to study our own cosmic backyard can be pointed outward with real precision.

[00:19:54]It's also worth acknowledging how this story has played out publicly because the gap between the careful incremental language used in peer-reviewed papers and the more dramatic language that circulates online has occasionally caused confusion. Headlines describing the object as anomalous or massive or ancient are not on their own inaccurate.

[00:20:11]The underlying data genuinely supports language like this. But it matters to distinguish between confirmed measurements like the presence of carbon dioxide, water, and methane, which multiple independent instruments have directly detected, and interpretive conclusions like the exact age of the comet or the full explanation for its apparent mass anomaly, which remain active areas of ongoing research and in some cases genuine scientific disagreement. Responsible science communication holds both of these truths at once. The discoveries are genuinely extraordinary. Some of the most remarkable data ever collected about a visitor from beyond our solar system.

[00:20:45]And at the same time, some of the boldest interpretations of that data are still being tested, challenged, and refined by researchers around the world exactly as the scientific process is designed to work. Putting the full picture together, what we actually know and what remains uncertain, tells a genuinely compelling story on its own without needing to reach for anything beyond real science. 3i Atlas is the third confirmed interstellar object ever detected passing through our solar system. And by far the largest and most massive of the three found so far with a solid nucleus now measured at approximately 2.6 km across. Tens of times more massive than Umuamua and Borosov. It is releasing gas dominated overwhelmingly by carbon dioxide in a ratio to water so extreme that it stands apart from nearly every other comet ever measured. And it is doing so alongside detectable water, carbon monoxide, cyanide, atomic nickel, and in a first for any known interstellar object, methane. Its outgassing behavior has produced a mass anomaly significant enough that at least one prominent research team believes the comet may be more massive than its visible activity alone would predict. A claim still being debated and tested by the wider scientific community. and its likely formation sometime in the first several billion years of the Milky Ways history would make it one of the oldest solid objects ever directly studied by human instruments. A genuine time capsule from an era of the galaxy that existed long before our own sun was born. The object continues to move, having passed its closest approach to the sun. Three Atlas is now on its way back out, following a hyperbolic trajectory that will carry it beyond the reach of our telescopes and eventually beyond the solar system entirely, never to return. NASA has coordinated observations across multiple missions to make the most of this narrow window while it remains visible, including continued monitoring from Hubble as the comet departs alongside data already gathered by Spherex and Infrared Observatory that mapped the Coma's dust, water, organic molecules, and carbon dioxide, and by TESS, better known for hunting planets around other stars, which was redirected to study the comet's rotation and activity. Each of these instruments has contributed a different piece to a single expanding picture, and researchers will likely spend years analyzing the data already collected long after the comet itself has faded from view. There's also a quieter, more human dimension to this story that rarely makes it into the headlines. Behind every measurement described here sits a team of researchers who had to drop other projects, rewrite proposals, and analyze incoming data on an accelerated timeline, all while knowing the window to study this particular object would never reopen. Martin Cordinire, an astrochemist at NASA's Gddard Space Flight Center, who led the team behind the origin study, described the moment as a unique opportunity to study an object that likely predates our own sun and solar system entirely, offering direct insight into a distant time and place that would otherwise be completely unreachable. That sense of urgency, of racing to extract every possible piece of information before a once in a generation visitor slips back into the dark, runs through nearly every published account of this research. It is a reminder that behind the graphs, the spectra, and the size estimates, this is fundamentally a story about scientists working quickly and carefully to answer questions that may not get another chance to be asked for decades or possibly longer. What makes this moment worth pausing on isn't just the numbers, striking as they are, it's the sheer improbability of the opportunity itself. For all of recorded human history and for the 400 years since Galileo first turned a telescope toward the sky, we had never once confirmed direct physical evidence of material from another star system passing through our own. Then within the span of 8 years, we found three. And the third one threeey atlas arrived large enough, active enough, and close enough for our best instruments. instruments built specifically to peer through cosmic dust and read the chemical history hidden inside it to actually study it in real detail. Whatever this object turns out to fully explain about its own origin, about the conditions in some distant ancient corner of our galaxy where it first froze into existence, one thing is already certain. For a few short months, a fragment of the early universe drifted through our solar system, warmed briefly by our sun, and let us read its story before continuing on a journey that began billions of years ago and will now carry it back into the dark. This time for good.