NASA has now confirmed that 3I/ATLAS is not just another visitor from deep space but the largest interstellar comet ever measured, a frozen fragment of another star system sweeping through our own. Its sheer scale, unusual orbit, and comet-like behavior are giving scientists an unprecedented chance to compare a truly alien iceberg with the familiar comets that loop around our Sun.
As researchers race to observe 3I/ATLAS before it disappears back into interstellar darkness, the object is rapidly becoming a touchstone for questions about how planetary systems form, evolve, and eject debris. I see this comet as a rare natural probe, one that is already reshaping how astronomers think about the population of wandering bodies that drift between the stars.
How 3I/ATLAS crashed the interstellar record books
Interstellar objects are, by definition, outsiders, but 3I/ATLAS has forced its way to the front of the line by sheer size. Only three confirmed visitors from beyond the Sun’s gravitational family have ever been identified, and Comet 3I/ATLAS is only the third known object to pass through our solar system from interstellar space, following 1I/ʻOumuamua and 2I/Borisov. That alone would make it historic, yet what sets it apart is that NASA now recognizes it as the biggest interstellar comet on record, with a nucleus far larger than anything inferred for its predecessors, a status that immediately elevates it from curiosity to cornerstone in the study of alien small bodies.
NASA’s dedicated science page on the object frames 3I/ATLAS as a fully fledged comet, not a mysterious shard or ambiguous rock, emphasizing that it looks and behaves like the icy bodies that routinely fall inward from the outer Solar System. The agency’s overview of Comet 3I/ATLAS situates it within a broader effort to catalog and understand such visitors, tying its discovery to ongoing sky surveys that scan for potential impact threats and unexpected interlopers alike.
What makes an object truly interstellar
To understand why 3I/ATLAS is classified as interstellar, I have to start with its trajectory. The comet follows a hyperbolic path that is not bound to the Sun, meaning its eccentricity is greater than 1 and it will never settle into a closed orbit. Analyses of its motion show that it is traveling fast enough that the Sun’s gravity can only bend its course, not capture it, a clear signature that it originated outside the Solar System and is simply passing through before heading back into the galactic background.
That hyperbolic orbit is not just a mathematical curiosity, it is the key evidence that 3I/ATLAS was born around another star. Earlier interstellar visitors like 1I/ʻOumuamua and 2I/Borisov were identified in the same way, with their paths revealing that they could not have been flung out from any plausible reservoir of local comets. NASA’s own Facts and FAQS on Comet 3I/ATLAS underline that it is only the third such object ever found, a reminder of how rare these detections are even in an era of powerful surveys.
How big is “biggest”: Hubble’s size estimate
Calling 3I/ATLAS the largest interstellar comet is not a matter of guesswork, it rests on direct measurements of its solid core. The Hubble Space Telescope has been trained on the object, and Hubble’s observations are allowing astronomers to more accurately estimate the size of the comet’s solid icy nucleus by separating the bright surrounding coma from the central body. By modeling how sunlight reflects off that nucleus and how the coma spreads outward, researchers can infer both its diameter and its reflectivity, which together point to a bulkier object than either 1I/ʻOumuamua or 2I/Borisov.
Those Hubble data also open a window into the comet’s composition, since the way the coma brightens and the gases disperse reveal what is sublimating off the surface. The early conclusion is that 3I/ATLAS is a “really weird, big object,” in the words of scientists who are trying to reconcile its size with its activity level and orbital history. The detailed breakdown of how Hubble is being used here underscores just how much effort is going into pinning down the physical reality behind the record-breaking label.
Comparing 3I/ATLAS with ʻOumuamua and Borisov
Size alone would make 3I/ATLAS stand out, but the comparison with earlier interstellar visitors is even more revealing. So far scientists have discovered only three such objects, and 1I/ʻOumuamua and 2I/Borisov set the initial template for what these wanderers might look like. How 3I/ATLAS differs from 1I/ʻOumuamua and 2I/Borisov is central to the story: aside from being significantly more hyperbolic, the most striking distinction is that 3I/ATLAS presents as a classic comet with a substantial nucleus and a robust coma, whereas ʻOumuamua was small, oddly shaped, and lacked a clear tail, and Borisov was more modest in scale.
That contrast suggests that the population of interstellar objects is far more diverse than the first two examples implied. The new comet’s larger size and more conventional appearance hint that 1I/ʻOumuamua might have been an outlier rather than the rule, while 2I/Borisov may represent the smaller end of a broad size distribution. A detailed overview of what is currently known about this rare cosmic visitor notes that these differences could change with more observations, but already the catalog of Oumuamua and Borisov versus 3I/ATLAS is forcing theorists to widen their expectations for what gets ejected from distant planetary systems.
Why astronomers say this is a “really weird, big object”
Even within the category of comets, 3I/ATLAS is not behaving in a completely routine way. Before the comet swings past the Sun and disappears from view, a team led by David Jewitt at the University of California, Los Angeles is racing to pin down its properties, from rotation to outgassing patterns. Jewitt and his colleagues have described it as a “really weird, big object,” a phrase that captures both its scale and the fact that its activity does not line up neatly with standard models of how a comet should respond to solar heating at different distances.
Part of that weirdness lies in the balance between its enormous nucleus and the level of gas and dust it is shedding. For an object with such a large core, the coma and tail are not as overpowering as some astronomers expected, which raises questions about how its surface has evolved in the harsh environment of interstellar space. The ongoing campaign to study these mysteries is laid out in a set of biggest mysteries surrounding 3I/ATLAS, and those puzzles are exactly what make this comet such a valuable test case for theories of how icy bodies age between the stars.
Orbit, eccentricity and the “alien technology” debate
Whenever an object from outside the Solar System appears, speculation about exotic origins is never far behind, and 3I/ATLAS is no exception. Additionally, the comet exhibits some remarkable properties distinguishing it from its predecessors. First, the eccentricity of its orbit is extremely high, reflecting a trajectory that is more sharply hyperbolic than either ʻOumuamua or Borisov, and second, its physical scale, with a width of over 20 km, makes it a genuine giant among known interstellar bodies. Those two facts together have fueled both serious scientific analysis and more speculative chatter about whether such objects could ever be artificial.
Researchers who have looked closely at the data, however, see a natural explanation that fits comfortably within current models of planetary system evolution. The same processes that can eject smaller fragments like ʻOumuamua can also hurl out much larger icy bodies, especially during the early, chaotic stages when giant planets are migrating and scattering debris. A detailed comparison of 3I/ATLAS and Oumuamua that asks whether they are comets or alien technology concludes that the observed eccentricity and the width of over 20 km are entirely consistent with a natural cometary origin, and that the object’s behavior matches what would be expected from a large, volatile-rich body rather than any kind of engineered craft, as laid out in the analysis of 3I/ATLAS and Oumuamua.
How 3I/ATLAS behaves near the Sun
One of the strongest arguments that 3I/ATLAS is a conventional comet, albeit an interstellar one, comes from how it responds to solar heating. As it travels through the inner Solar System, the object has developed a coma and tail that brighten and evolve in ways that closely resemble Sun-bound comets that originate within our Solar System. Observers tracking its path report that 3I/ATLAS is traveling through the planetary region on a trajectory that will carry it past the Sun by early December, and its activity curve as it approaches and recedes from that perihelion looks strikingly familiar.
This behavior matters because it ties the comet’s physics to well-understood processes like sublimation of water ice and other volatiles, rather than to any exotic mechanism. The fact that its outgassing ramps up in step with increasing solar energy, and that its dust tail responds to the solar wind and radiation pressure in textbook fashion, reinforces the conclusion that we are seeing a natural object obeying the same rules as local comets. The European and NASA teams that have monitored this evolution describe how 3I/ATLAS is traveling through the inner system, and their reports of its Sun-like behavior are a key pillar of NASA’s decision to label it definitively as a comet.
NASA’s verdict: it “looks and behaves like a comet”
NASA’s public messaging around 3I/ATLAS has been unusually direct, reflecting both the public fascination with interstellar visitors and the need to tamp down unfounded speculation. During a recent briefing, mission leaders emphasized that the object looks and behaves like a comet, with a clear coma, a dust tail, and activity that tracks its distance from the Sun. They stressed that there is no credible evidence that it is anything other than a natural icy body, and that its interstellar origin is established by its orbit, not by any exotic properties.
That clarity is important because it anchors the narrative in observable facts rather than in conjecture. NASA officials have also highlighted the way multiple spacecraft and observatories across the Solar System are contributing images and spectra, building a composite portrait of the comet from different vantage points. Coverage of the agency’s latest image release notes that NASA reveals new images that reinforce this message, showing a classic cometary profile that would look at home in any atlas of Solar System comets despite its alien origin.
What NASA’s latest briefing revealed about the comet
Beyond the headline that 3I/ATLAS is the largest interstellar comet yet seen, NASA’s latest science briefing filled in crucial details about its composition, structure, and long-term trajectory. Officials outlined four key findings, including confirmation that the object is rich in volatile ices, that its nucleus is far larger than those of previously known interstellar visitors, that its orbit is unambiguously hyperbolic, and that its activity profile matches that of a natural comet. They also emphasized that the data set is still growing, with new observations scheduled as the comet recedes from the Sun and its activity wanes.
For me, the most striking element of that briefing was how quickly 3I/ATLAS has gone from a faint moving dot in survey images to a well-characterized physical object with a defined place in the taxonomy of small bodies. The agency’s summary of what it has just revealed about the interstellar comet underscores that the consensus is now firm: 3I/ATLAS is a comet, not an asteroid or anything more exotic, and its record-breaking size makes it a benchmark for future discoveries. The rundown of 4 key things NASA just revealed captures how much has been learned in a short time, and how that knowledge feeds into broader models of interstellar debris.
From ATLAS survey to global spotlight
Long before it became a household name among space enthusiasts, 3I/ATLAS was simply another detection in a sky survey designed to spot potentially hazardous objects. The comet was discovered by the Asteroid Terrestrial-impact Last Alert System, a network whose very name, Asteroid Terrestrial and Last Alert System, reflects its role in scanning the skies to keep us safe from incoming threats. In this case, the system flagged an object whose motion did not fit the pattern of a typical near-Earth asteroid, triggering follow-up observations that quickly revealed its interstellar nature and cometary activity.
Once its status was clear, the comet was formally designated 3I/ATLAS, also known as C/202…, placing it in the same naming scheme as Comet ATLAS and other discoveries from the same survey. That label encodes both its order in the sequence of interstellar objects and its origin in the ATLAS program, which has become a quiet workhorse of planetary defense and small-body science. The entry for 3I/ATLAS notes that it follows 1I/ʻOumuamua and 2I/Borisov in the interstellar catalog, and that connection to a systematic survey effort is a reminder that record-breaking discoveries often emerge from infrastructure built for more routine, but vital, monitoring.
Why this giant interstellar comet matters for planetary science
The scientific payoff from 3I/ATLAS extends far beyond the thrill of setting a new record. Because it is so large, the comet preserves a substantial volume of primordial material from its home system, material that has been shielded in its interior from radiation and collisions for eons. By analyzing the gases and dust it releases, astronomers can compare its chemistry with that of comets formed around the Sun, looking for similarities and differences that might reveal how common our own recipe for planet building really is in the galaxy.
That comparison is already underway, with teams examining spectral lines from water, carbon-bearing molecules, and more complex organics in the comet’s coma. If 3I/ATLAS turns out to have a composition broadly similar to Solar System comets, it would support the idea that the basic ingredients for planets and potentially for life are widespread. If it proves to be chemically unusual, that would be just as interesting, pointing to diversity in how planetary systems assemble and evolve. NASA’s official science hub for the comet, which is linked from a widely shared clip noting that Below are the official links so you can see everything for yourself, directs interested readers to NASA’s Official 3I/ATLAS Science Page, where those compositional studies and their implications for planetary science are being tracked in detail.
More from MorningOverview