the comet 3I/ATLAS has earned a place in the history of astronomy such as Third interstellar visitor confirmed that passes through our Solar System. Its fleeting passage has left behind an avalanche of scientific data that goes far beyond a simple cosmic anecdote: from its chemistry rich in organic molecules to jets of gas and dust that reveal how its icy core rotates.
Far from being a simple blurry dot in the sky, 3I/ATLAS has become a authentic natural laboratory to study matter from another star system. European observatories, with a prominent role played by facilities in Spain and the Canary Islands, have closely monitored its hyperbolic trajectory, its composition and its activity, taking advantage of the unique window offered by an object that, once it moves away, will not pass by again.
An interstellar visitor passing through our neighborhood
3I/ATLAS was officially identified on July 1, 2025 by the ATLAS alert system, based in Chile, and reported to the Minor Planet Center. Subsequent reviews of observational archives made it possible to locate previous images from mid-June, including data obtained from the Palomar Observatory in the United States.
El The closest approach to the Sun (perihelion) occurred on October 30, 2025, about 210 million kilometers from the star. Weeks later, the On December 19, 2025, it reached its closest point to Earth., around 269-270 million kilometers, a separation wide enough to rule out any risk, but close enough for telescopes to be able to make the most of it.
From the moment of its detection, NASA, ESA and numerous ground-based observatories They have tracked its movement and brightness. Its speed relative to the Sun is extremely high, typical of an object that is not "trapped" by solar gravity and is simply crossing our neighborhood before being lost again in interstellar space.
The chemistry of a comet that brings ingredients for life
One of the aspects that has attracted the most attention is the chemical composition of 3I/ATLASObservations made with the ALMA radio telescope between August and October 2025 have allowed for a detailed study of the gas released from the comet as it heats up while approaching the Sun.
The data shows that Methanol represents about 8% of the vapor releasedThis proportion contrasts sharply with that of typical comets in the Solar System, where this compound usually hovers around 2%. This difference suggests that the comet formed in an environment with chemical conditions somewhat different from those of our protoplanetary cloud.
In addition to methanol, Hydrogen cyanide and other molecules that are key to prebiotic chemistry have been detected.These substances participate in the formation of amino acids and sugars, precursors to fundamental structures such as DNA and RNA. The discovery reinforces the idea that the basic ingredients for life are not exclusive to our corner of the galaxy.
The analyses also indicate the presence of water ice inside the cometThe ice, combined with organic compounds and other volatile species, makes 3I/ATLAS a particularly valuable tool for understanding how the elements essential for biology can be distributed throughout the galaxy. All this, without needing to leave our own star system.
The teams that have led these observations insist that, despite the striking nature of their chemistry, There is no evidence of an artificial origin or technologicalIt is a natural body, ejected from its system of origin and preserved for billions of years in the cold interstellar space until its encounter with the Sun.
Oscillating jets and an anti-tail pointing towards the Sun
If the chemical composition was already interesting, The activity of 3I/ATLAS has proven even more surprisingSeveral observation campaigns have detected a narrow jet of gas and dust that originates in the area illuminated by the Sun and that periodically changes orientation, distinct from the conventional dust tail that extends in the opposite direction to the star.
This pattern has been observed in particular detail thanks to the Two-meter Twin Telescope (TTT), a robotic telescope located at the Teide Observatory in TenerifeThe experiment, operated by Light Bridges in collaboration with the Instituto de Astrofísica de Canarias (IAC), monitored the comet's evolution for 37 nights between July and September 2025 using specific processing techniques to highlight the internal coma and low-intensity structures.
The results show a narrow structure oriented towards the illuminated regionWhile the classic dust tail extends in an antisolar direction. Viewed from Earth, this configuration gives rise to what is known as an “antitail”: a tail that, due to perspective and orbital geometry, appears to point towards the Sun even though the particles are still being pushed in the opposite direction by radiation and the solar wind.
During several nights in August, they were clearly detected jets that oscillated with a regular motionThis "dance" of ejected material, visible in the antitail itself, constitutes the first evidence of localized and repetitive activity in a comet of interstellar origin. This has been observed in comets within our own solar system, but never before in a visitor from another star.
How the 3I/ATLAS core rotates
The oscillation of these jets is not just a curious detail: has allowed us to measure the rotation period of the comet's nucleusBased on the rate at which the jet's orientation changed, astronomers have estimated that the core of 3I/ATLAS completes a rotation on its axis in about 14-17 hours, with analyses that refine the value to around 15 and a half hours.
In comets, The activity depends largely on how solar heat affects specific regions of the coreWhen an ice-rich region transitions from darkness to light, the material heats up, sublimates, and draws in dust, generating jets that can appear and disappear as the comet rotates. If the active source is near a pole, the apparent variation of the jet will be gentler; if it is located at mid-latitudes, the ebb and flow becomes much more pronounced.
The data obtained with the TTT fits well with this image: a relatively stable core with one or more localized active zones which produce a thin, persistent jet. The observed behavior, consistent with independent estimates, suggests that the comet's internal structure is not chaotic, but rather that of a body that maintains its integrity despite intense solar radiation.
All of this makes 3I/ATLAS the first interstellar comet whose rotation has been measured in detail from its own activityThis information is crucial for comparing their behavior with that of "domestic" comets and for improving models that explain how these bodies are activated and evolve as they approach a star.
The study of turnover also helps to assess the long-term stability of the core and its possible future fragmentationFor now, observations point to a surprisingly "normal" comet for a visitor from outside, which in science is usually good news because it allows us to apply known models in a new context.
Does the material ejected by the comet pose a risk to Earth?
The presence of cyanide and hydrogen cyanide in the gaseous envelope of 3I/ATLAS This has inevitably generated some concern outside the scientific community. It's not surprising that, coinciding with its closest approach, questions have arisen about whether some of that material could reach Earth and have any effect on our atmosphere or surface.
Calculations indicate that The gas emitted by the comet is quickly swept away by the solar windBased on the mass loss rate measured, for example with the James Webb Space Telescope, it is estimated that the gaseous cloud surrounding the comet is slowed down and dragged to distances of only a few million kilometers from the object itself, well inside Earth's orbit.
The Dust particles smaller than one micron are even more vulnerable to solar radiation pressureTherefore, they disperse and are deflected before they can follow a trajectory that intercepts Earth's orbit. At the opposite extreme, solid fragments of millimeter size or slightly larger are barely affected by the solar wind, but their number is limited and the probability of any of them reaching our planet is extremely low.
Even if small particles from 3I/ATLAS were to enter the atmosphere, Normally they disintegrate completely before reaching the groundprovided their size is well below one meter in diameter. What we would see from Earth, at best, would be very faint meteors associated with a weak flow of interstellar dust.
However, this situation opens up an interesting possibility from a scientific point of view: to collect millimeter-scale particles using experiments in orbitFor example, on satellites or the International Space Station, above the densest layers of the atmosphere. Capturing and directly analyzing material shed from an interstellar comet would be a significant leap forward in studying its composition without relying solely on the light it reflects or emits.
Europe, and especially Spain, on the front line of observation
The passage of 3I/ATLAS has highlighted the importance of the network of European observatories to study rapid and infrequent phenomena such as the visit of an interstellar comet. Spain, thanks to its geographical position and the quality of its skies, has played a particularly important role.
From the peaks of Tenerife, the Teide Observatory and the Two-meter Twin Telescope have achieved image sequences which have allowed us to discover and characterize the oscillating jet, infer the rotation period of the nucleus and follow the evolution of the coma and the antitail over more than a month of intensive campaigning.
On the Peninsula, facilities such as the Montsec Astronomical Observatory in CataloniaThey have contributed complementary observations that help reconstruct the brightness and overall activity of the comet. Although some preliminary results on very exotic compositions are still under review, coordination between Spanish and European centers is proving key to refining the models.
Even smaller observatories, such as the Z39 Observatory in Lanzarote, accredited by the Minor Planet CenterThey have contributed images and videos that visually illustrate the rapid movement of 3I/ATLAS against the starry background. These contributions not only have scientific value but also a strong educational component, bringing to the public a phenomenon that, despite its cosmic scale, has been closely followed from European soil.
The coordinated effort between large professional telescopes and more modest observatories demonstrates How European astronomy can react quickly to transient eventsmaximizing the scientific return on visits that, like that of 3I/ATLAS, will not be repeated.
What 3I/ATLAS tells us about other planetary systems
Beyond curiosity about a "foreign" visitor, The deep interest in comets like 3I/ATLAS is comparableEach of these objects offers a direct sample of material that formed around another star, under conditions that may differ, to a greater or lesser extent, from those that gave rise to our Solar System.
By analyzing its nucleus, its comma, and its tails, Astronomers can test the extent to which planetary formation processes are universal.The proportion of organic molecules, the abundance of water ice, or the way the surface is activated when it receives radiation helps to reconstruct the original environment in which the comet clumped together.
3I/ATLAS thus joins the short list of known interstellar visitors, but it does so with a level of observational detail without precedentsPhotometric, spectroscopic and deep imaging campaigns have made it possible to characterize its rotation, its mass loss rate and its geometric peculiarities with a precision unthinkable just a few years ago.
As ground-based telescopes and early warning systems improve, More comets and asteroids from other star systems are expected to be detected.Each new object will allow us to check whether the properties of 3I/ATLAS are common or whether, on the contrary, we are dealing with a particularly unique case within a very diverse population.
As the comet moves away into interstellar space, The data collected will continue to be a goldmine for the scientific community For a long time, 3I/ATLAS has served to refine observation techniques, test models of cometary activity and, above all, remind us that the chemical building blocks of life and the physical mechanisms that shape comets do not understand borders between star systems.
