The interstellar object 3I/ATLAS It has slipped onto the agenda of world astronomy as one of the most unsettling and fascinating visitors of recent years. It arrived from outside the Solar System, crossed the Oort Cloud, and is now heading for a very close encounter with Jupiter that, if everything goes according to plan, will turn March 2026 into a true test of our theories about comets, gravitational capture, and even possible technological signatures.
An interstellar traveler with a scheduled appointment in Jupiter's neighborhood
3I/ATLAS is the third interstellar object identified crossing our Solar System, after 'Oumuamua and 2I/Borisov. It did not form here and, unless something extraordinary deflects it, will never returnIts journey began about 100.000 astronomical units from the Sun, on the periphery of the Oort Cloud, and since then it has been losing energy until it slipped into the region where Jupiter's gravity begins to compete with that of the Sun itself.
The key point of this journey will arrive in March 2026. Orbital calculations, which include the small non-gravitational accelerations typical of comets, place 3I/ATLAS at about 53,6 million kilometers from Jupiter around March 16, practically on the edge of its Hill's sphere, the volume where the planet's attraction dominates against solar tides. It is a crossing at the edge of Jovian "gravitational territory," much tighter than usual for an interstellar object.
The following day, March 17, the historical record indicates another statistical coincidence: the comet will pass about 30 million kilometers from EuphemeA tiny, irregular moon of Jupiter, barely 2 kilometers in diameter, and a member of the so-called Ananke group. Although these distances are enormous on a human scale, for the architecture of the Jovian system they are surprisingly close encounters.
In dynamic terms, the passage of an interstellar body across the edge of the Hill sphere of a giant planet is a natural capture experimentIt is expected that 3I/ATLAS will curve, emerge somewhat disturbed, and continue out of the Solar System. But if it were to leave something behind—a fragment or "daughter" gravitationally bound to Jupiter—physicists would have to work very carefully to explain it.
Therefore, agencies and observatories are preparing for intense monitoring of the encounter. The probe Juno will monitor the planet's environment in situ, while the largest ground-based telescopes Europe and the rest of the world will coordinate to look for any changes in the brightness of the comet, fragmentations, or the appearance of new points of light linked to the Jovian system.
Eupheme, the irregular moons and a gravitational laboratory
In this scenario, a minor moon has gained an unexpected role: Eupheme, a member of Ananke's groupIt is an irregular, very faint satellite, whose estimated diameter is around 2 kilometers assuming a low albedo, typical of dark bodies. It belongs to a family of about fifteen Jovian moons with similar orbits.
These small moons move along trajectories very eccentric, slanted and retrogradeThat is, they rotate in the opposite direction to Jupiter's rotation and far from its equatorial plane. Everything points to them originating from the capture and fragmentation of a parent body which, at some remote point in time, was torn apart by a collision or by the tidal forces of the planet itself.
Eupheme takes about 588 days to complete an orbit around Jupiter. At the end of January 2026, it will reach its maximum distance from the planet, around 27,7 million kilometers, a few weeks before the closest approach of 3I/ATLAS. The fact that the interstellar object I passed so close to the region occupied by this family of moons It does not imply a danger of collision, but it does turn the area into a privileged laboratory for studying how an outside visitor interacts with a swarm of captured satellites.
With 95 cataloged Jovian moons And with a population of fragments yet to be surveyed, the odds of close encounters are not ridiculous. Even so, the specific configuration of March 2026—an interstellar body, a giant planet, and an irregular moon all on the same board—is rare and offers a unique opportunity to test our capture-scattering models.
The “96th moon” that physics doesn’t know how to make
This encounter with Jupiter has formed the basis of one of the most controversial hypotheses surrounding 3I/ATLAS. The astrophysicist Avi LoebA professor at Harvard has proposed a very simple criterion to verify: if after the encounter a new moon appears linked to JupiterWith an orbit consistent with a recent capture from the comet, we would have to seriously consider whether we are facing a sign of artificial intervention.
Currently, the catalog includes 95 known satellites around JupiterLoeb speaks of the hypothetical “96th moon” as a kind of technology firmAn object that doesn't dynamically fit with what nature can produce on its own. His argument is based on numbers, not exotic assumptions.
At the point of closest approach, the relative speed The speed between 3I/ATLAS and Jupiter will be about 66 kilometers per second. At that distance, the escape velocity from Jupiter's gravitational field drops to about 2,2 km/s. For a fragment of the comet to go from sharing the motion of the main body to becoming trapped in a stable orbit, it would need a velocity "push" on the order of tens of kilometers per second, adjusted with extreme precision in module and direction.
The natural processes that cause comet fragmentation—tidal breakups, internal volatile explosions, collisions—generate relative separation speeds in meters per secondPerhaps tens of kilometers per second in extreme events, but not kilometers per second. Not even Jupiter, with its enormous mass, can impart that extra energy to an individual piece without completely destroying it.
Hence, Loeb concludes that the window for a piece of 3I/ATLAS to end up as a new moon is extraordinarily narrow for any natural settingIf, despite everything, the encounter confirms the existence of a new satellite with the appropriate dynamic characteristics, the very design of the test would force a re-evaluation of what might be behind it: a calculation error, some previously unconsidered physics, or, at the extreme, deliberate intervention. If nothing is found, the hypothesis would be definitively disproven.
An “extraordinarily normal” comet… with a very particular jet
While orbital dynamics grabs headlines, another line of research focuses on the Physical activity of the 3I/ATLAS coreHere, European observatories have played a prominent role. At the Teide Observatory in Tenerife, the Two-meter Twin Telescope (TTT) led an intensive observation campaign between July and September 2025, within the framework of the PLANETIX25 project.
The team from the Canary Islands Institute of Astrophysics (IAC) detected for the first time a jet of gas and dust well-defined coming out of the core of this interstellar comet, along with a periodic modulation associated with the body's rotation. Using image processing techniques—such as the Laplacian transform applied to the internal coma—they were able to highlight a faint but real structure that vibrates slightly around the rotation axis.
That behavior allowed Estimate the core rotation period to be between 14 and 17 hours, in line with previous measurements obtained with the TTT itself, the Canary Islands Great Telescope and the Complutense University of Madrid. For the Canary Islands researchers, what is striking is not so much the rarity of the object as its familiarity: 3I/ATLAS behaves, in many respects, like a “normal” comet Of the solar system.
That is precisely why characterizing this jet in detail is so valuable: It offers a direct comparison. between the physics of a pristine nucleus, formed in another planetary system, and the comets we know at home. The structure of the jet, its evolution with distance from the Sun, and its response to the nucleus's rotation provide clues about the distribution of ices, active cracks, and sublimation processes in an object that has spent billions of years traveling through interstellar space.
Beyond the Canary Islands, the Hubble Space Telescope has added another piece to the puzzle. Her in-depth images have revealed something even more perplexing: a jet or annealus oriented towards the Sun and extremely collimated, with a length of up to about 400.000 kilometers, comparable to the Earth-Moon distance, which defies expectations about how the ejected material should respond to the pressure of the solar wind.
Hubble's anticauda and improbable alignments
The latest Hubble image, taken on January 7, 2026, has intensified the debate. After applying a rotational gradient filter that attenuates the symmetrical structures of the coma, a triple jet configurationThe most striking is a narrow, bright beam that points almost directly towards the Sun, flanked by two secondary jets that open up on either side at a similar angle.
In a conventional comet, the dominant structure is a tail that extends away from the Sun, pushed by radiation pressure and the solar wind. In 3I/ATLAS, however, The most intense structure advances against that wind.While the "classic" tail extending outwards is barely noticeable. The length and collimation of the main beam, in Loeb's words, are more reminiscent of a system of well-aligned nozzles than a chaotic exhalation of gas and dust.
The same researcher has drawn attention to another geometric coincidence. Starting from the observed jet wobble At different points in his career, along with his collaborator Eric Keto, he has inferred that the The 3I/ATLAS rotation axis points towards the Sun with an accuracy better than a few degrees when the object is far from the star. In parallel, the comet's orbit is very close to the plane of the ecliptic, the plane in which the planets orbit.
If we assume that the possible orientations are random, the probability that the axis of rotation points almost directly at the Sun is low on its own; and the same is true of the trajectory being so close to the ecliptic. Combined, The odds fall below one in ten thousandAccording to estimates published by Loeb, this is not proof of anything in itself, but it does serve as a reminder that the geometry of the system deserves more than just a footnote.
In fact, that's where the disagreement with the official narrative emerges. In a press conference in November 2025, NASA spokespeople They presented 3I/ATLAS as a natural comet without major surprises, glossing over these anomalies. For Loeb, this contrast between the data and the way it is communicated illustrates a broader problem: how the scientific community decides which phenomena deserve attention and which are filed away as obscure oddities with no future.
Alongside the academic discussion, the case has also reached the offices of US intelligence agencies. A CIA response to a request for access to information about 3I/ATLAS was limited to “neither confirm nor deny” the existence of related documentsThis is an unusual formula applied to an astronomical object. For some analysts, this suggests that, although the probability of a threat is extremely low, the potential impact of a technological "black swan" necessitates close monitoring of the matter.
Search for techno-firms: silent radio and open experiments
Given such a peculiar object, it was only a matter of time before someone looked at 3I/ATLAS through the lens of SETI. The program breakthrough listen, which uses world-class radio telescopes to search for technological signals, dedicated several hours of observation to the interstellar visitor using the Green Bank radio telescope, in United States.
The goal was simple: to track narrowband radio signalsThis type of transmission is very efficient for communicating over long distances and is rarely produced spontaneously by nature. Data in the 1 to 12 GHz range were analyzed during a five-hour window on December 18, 2025, in search of transmissions that could be associated with the comet.
The result was negative. No artificial intelligence-compatible signal was detected from 3I/ATLASThe few candidate events that appeared in the initial screening were ultimately attributed to terrestrial interference. For many astronomers, this outcome aligns with the idea that we are dealing with a natural comet which, although unusual in some aspects, is neither a spacecraft nor an interstellar beacon.
Other researchers, however, qualify what can be concluded from this type of search. Given that An interstellar object takes tens of thousands of years to cross the galaxyWhile their stay in the Solar System lasts about 16.000 years round trip from the Oort Cloud, the probability of catching a transmission directed directly toward Earth in a window of only five hours is minuscule. Furthermore, an advanced civilization could use other frequency bands, very brief modulations, or extremely targeted beams that are not aimed in our direction.
In that context, the absence of radio technology companies does not close the case, but narrows the space of possibilitiesWhat is clear is that the dynamic experiment of March 2026 —to see whether or not that hypothetical “96th moon” appears— is a much more direct test: either there is a new satellite with parameters impossible to reproduce naturally, or there isn't.
That philosophy of “falsifiable evidenceThis is precisely the approach Loeb advocates for tackling uncomfortable questions without abandoning the scientific method. It involves presenting concrete scenarios where data can clearly support or refute the most daring ideas without resorting to gratuitous speculation.
The role of Europe and Spain in the monitoring of 3I/ATLAS
Beyond the theoretical controversy, the 3I/ATLAS case is also serving to to highlight European observation capabilitiesThe work of the IAC and the Teide Observatory is a close example: a 37-night campaign with the TTT, supported by computing infrastructures such as ASTRO POC, has made it possible to extract very high-level information about an extremely faint and distant object.
To this must be added the contribution of large facilities such as the Gran Telescopio Canarias (GTC), the world's largest optical-infrared telescope, or the Very Large Telescope (VLT) from ESO in Chile, where numerous European teams are working. These instruments are key to unraveling the composition of the gas and dust in 3I/ATLAS, measuring variations in brightness, and tracking the evolution of its activity as it moves away from the Sun.
In space, Europe plays a decisive role in missions that, although not specifically designed to study this comet, have taken advantage of their passage to obtain valuable observations
The image captured by Europa Clipper, more than 160 million kilometers away, was obtained over a period of about seven hours, by breaking down ultraviolet light into different wavelengths to identify gases and chemical elements in the comet's comaThese types of observations complement those of optical telescopes from the ground, providing sensitivity to species that are not visible in the visible spectrum.
In the coming months, it is expected that other major European observatories coordinate monitoring campaigns around the date of closest approach to Jupiter. The objective will be twofold: on the one hand, to monitor any sudden changes in the activity of 3I/ATLAS; on the other, to monitor the Jovian neighborhood in search of new components in its already complex system of satellites.
Overall, the story of 3I/ATLAS has become a good barometer of how The European and Spanish scientific community is integrating into global observation networksproviding key data and sophisticated analysis in near real time on phenomena that, until recently, seemed like mere science fiction.
With all this attention, the small interstellar visitor has gone from being just another point of light in the annals of celestial events to a case study that touches on almost every aspect: extreme orbital dynamics, cometary jet physics, the search for technosignatures, and institutional management of the risk of cosmic "black swans." What happens—or doesn't happen—around Jupiter in March 2026 will help clarify the extent of this phenomenon. The explanation for 3I/ATLAS fits comfortably into the category of a natural comet or if, at least, it will force us to review some assumptions we thought were settled about these travelers of ice and dust.
