The new observation campaign adds to the new data about the comet collected by other missions, such as JUICE and PsycheIn a coordinated effort to make the most of 3I/ATLAS's brief stay in our cosmic neighborhood, scientists are taking advantage of every opportunity to measure its brightness, composition, and how the ice in its core transforms into jets of gas and dust as it heats up. Although it poses no threat to Earth, scientists are using every available window to observe its activity.
New Hubble images: a high-speed visitor
In the new footage, a teardrop-shaped dust cocoon that surrounds the frozen core, the so-called comaalong with a tail structure shaped by sunlight and the solar wind. Because the telescope had to track the comet's movement across the sky, the background stars appear stretched in the form of luminous streaks, while 3I/ATLAS remains the sharp point in the center of the scene.
Although Hubble cannot directly resolve the solid coreAstronomers have used the brightness and extent of the coma to constrain its maximum sizeEstimates suggest that the core would not exceed about 5,6 kilometers in diameter and it could be quite small, a modest size but more than enough to produce the intense jets observed when its surface is heated.
Those jets of gas and dustThese structures, generated by the sublimation of ice (the direct transition from solid to gas), are visible in the images as fine structures emerging from the nucleus and feeding the coma and tail. These details, which can only be observed with telescopes outside the atmosphere like Hubble, allow scientists to study how volatile material is distributed and how it changes over time as the comet rotates.
The first Hubble space observations had already been made July 21tha few weeks after the comet's discovery. At that time it was located about 277 million miles (approximately 445 million kilometers) and it already showed a well-defined dust envelope. From that moment, the space agency launched a prolonged follow-up campaign to study its evolution before, during and after perihelion, the point of closest approach to the Sun.
An interstellar comet closely monitored by NASA and ESA
3I/ATLAS was detected on July 1, 2025 through the early warning system ATLAS, a NASA-funded network of telescopes operating in Chile and Hawaii to locate potentially dangerous objects. In this case, the discovery did not involve any risk, but the third confirmed example de interstellar object that runs through our system, after 'Oumuamua in 2017 y 2I/Borisov in 2019.
From Europe, the European Space Agency (ESA) It has also played a significant role. The mission JUICE (Jupiter Icy Moons ExplorerThe spacecraft, which is traveling toward Jupiter to study its icy moons starting in 2031, took advantage of its trajectory to observe the comet. During the month of November, it activated five scientific instruments —among them JANUS, MAJIS, UVS, SWI and PEP— and their NavCam navigation cameraobtaining images and data about the coma, tails, and the plasma environment of 3I/ATLAS.
A preliminary image taken on November 2th 2025Two days before JUICE's closest approach to the comet, it already clearly showed the bright gas halo and clear clues to the presence of two tailsOn the one hand, a plasma tail, formed by ionized gas carried by the solar wind, and by another a dust tail fainter, composed of tiny solid particles that extend in another apparent direction.
The close encounter of JUICE with 3I/ATLAS occurred at approximately 66 million kilometers awayA safe separation, ideal for collecting detailed data on the interaction between the comet and the solar environment. However, the transmission of all the information is slower than usual because the spacecraft is using its main antenna as a heat shieldso communication now depends on a medium gain antenna with a much lower flow rate.
For this reason, ESA expects that the complete data packages from the scientific instruments will arrive on Earth over the course of February 2026Until then, the scientific community only has a fraction of the visual information, but enough to confirm that it is a very active comet after its passage through the inner region of the solar system.
In addition to Hubble and JUICE, NASA has mobilized other missions. The probe psyche, en route to the metallic asteroid of the same name, dedicated eight hours of observation On September 8th and 9th, the 3I/ATLAS telescope was used to track the reflection of sunlight. Its multispectral sensor allowed for fine-tuning the trajectory of the comet and study its more closely faint comaproviding complementary data to that collected by the telescopes.
What the images reveal about the comet's nucleus and activity
Hubble's high-resolution observations offer a privileged window into the internal structure and the comet's activity. Thanks to its position outside the atmosphere, the telescope can clearly distinguish the jets of material that are released from the core, something that is much more difficult from ground-based telescopes due to air turbulence.
These jets are essential for measure the chemical composition From 3I/ATLAS. By analyzing the light emitted by the ejected gases and dust, astronomers can determine what types of ices and volatile compounds the nucleus contains. The first results point to a chemical signature that matches that of other comets, although the fact that it is a object formed in another star system This makes it a natural laboratory for comparing differences and similarities with the bodies of the solar system itself.
The geometry and intensity of the jets also allow us to estimate the core rotation rateAs the comet rotates, the plumes of gas and dust change orientation, altering the distribution of brightness in the coma. By tracking these patterns in images taken on different dates, teams can reconstruct how the comet rotates and predict how its activity will vary in the coming months.
Another key aspect is how the expulsion of material affects the comet orbitThe forces called non-gravitationalThe gravitational forces generated by the jets' reaction as they are ejected can slightly deflect their trajectory compared to what would be obtained if only the gravity of the Sun and planets acted upon them. Hubble data help refine these deviations, improving the accuracy of orbital predictions as 3I/ATLAS moves away from the solar system.
The images taken around the perihelionAt the end of October, they show how activity increases with proximity to the Sun: the sublimation rate increases, the coma expands, and the queue is reconfigured due to the pressure of radiation and the solar wind. In the following weeks, during November and early December, the comet gradually lost brightness, reaching around magnitude 12, which makes it inaccessible to the naked eye and reserves it for medium or large-sized telescopes.
Despite the spectacular nature of the images, the distance measurements make it clear that There is no danger to EarthThe closest estimates are around 269 million kma margin wide enough to rule out any risk of impact, with the added attraction of being able to study the object without interference.
Interstellar origin and the scientific debate
3I/ATLAS joins the short list of interstellar visitors known to us, a club that until now only included 'Oumuamua and Comet Borisov. Like them, it is believed that It was formed in another system and that it was ejected into interstellar space millions of years ago, after gravitational interactions with planets or stars in its region of origin.
The confirmation of its origin outside the solar system is supported by its hyperbolic trajectory and its high speedWhen he was detected, he was traveling at about 221.000 km/hThe speed of the comet has varied as it has approached the Sun. This type of orbit means that the comet will only cross the planetary region once before continuing its journey outwards, without becoming permanently bound to the Sun's gravitational field.
The rarity of these objects has generated, as already happened with 'Oumuamua, a debate about its natureSome more speculative interpretations, such as those of the astrophysicist Avi LoebThey have suggested that certain variations in brightness or unusual structures could be consistent with an artificial probe. There has even been talk of a kind of "luminous heartbeat" or a possible Sun-facing anticoma which would resemble a propulsion mechanism.
However, the scientific community specializing in comets He argues that, with the available data, it is not necessary to resort to exotic explanations. Phenomena such as anticomas, or tails apparently directed towards the Sun, can be explained by perspective effects and by the dynamics of the heavier dust in the orbital plane, something already observed in comets of the solar system itself.
Mission analyses such as the James Webb Space Telescope (JWST) and various ground-based telescopes have detected typical chemical signatures of volatile icesconsistent with a natural comet. The small anomalies in the orbit fit well with the forces produced by the gas jets, without the need to invoke engines, sails, or artificial guidance systems.
In this context, the new Hubble images reinforce the interpretation of 3I/ATLAS as a active “classic” cometeven if it comes from another corner of the galaxy. For many researchers, the key lies not so much in searching for extraordinary signals as in taking advantage of this unique visit to compare the chemistry and physics of its ices with that of the comets that we have known for decades.
As the comet moves away between the constellations of Virgo and LeoThe activity is gradually declining. Scientific teams are making the most of the observation window, combining data from Hubble, JUICE, Psyche, and other observatories, with the aim of reconstructing the history of the object and fit it into the larger puzzle of planetary system formation.
We are facing a small comet of interstellar origin, very active after its passage by the Sun, which offers an exceptional opportunity to test models of cometary activity and orbital dynamics in contexts different from our own, and to put some of the most powerful missions of NASA and ESA to work together before the visitor continues on its way and disappears, silently, into the interstellar darkness.
