The third interstellar object ever detected crossing our Sistema Solar, comet 3I/ATLAS, has become the focus of intense research after Spanish scientists recorded clear evidence of cryovolcanic eruptions on its surface. The observations, carried out in October 2025, were conducted at Observatório Montsec, at Catalunha, and reveal a dynamic and chemically complex celestial body, offering a rare window into the composition of distant star systems.
Discovered in July 2025 by the ATLAS astronomical survey system, at Chile, the comet travels at an impressive speed of 221 thousand kilometers per hour. Sua hyperbolic trajectory, which is not gravitationally bound to Sol, confirms its extrasolar origin. The observed phenomenon suggests a composition rich in volatile materials and primitive ices, similar to that of objects found in the most remote regions of our own system, such as Cinturão and Kuiper.
The eruptions intensified significantly as the comet approached Sol, reaching a distance of about 378 million kilometers. The expelled jets of gas and dust created visible spiral structures in its coma, the gaseous atmosphere that surrounds the core. Essa discovery does not pose any risk of collision with Terra, but it provides crucial data about the chemical conditions present in other corners of the galaxy.
Observation details on Observatório Montsec
The monitoring of comet 3I/ATLAS was a coordinated operation that gained a new level of detail with the images captured by Telescópio Joan Oró. Although the celestial object Embora has been tracked by astronomers since its discovery in July 2025, it was during its approach to perihelion, the closest point in its orbit around Sol, that its activity reached its peak. Perihelion occurred on October 29, 2025, when the comet was at a distance of 1.36 astronomical units from our star, which is equivalent to approximately 203 million kilometers.
The high-resolution images obtained by the Spanish observatory were unprecedented, clearly capturing the jets of material being expelled from the comet’s nucleus. Esses records were essential for researchers to analyze the morphology and dynamics of the eruptions. The work of Observatório Montsec was complemented by a network of regional observatories on Espanha, which helped track the evolution of the comet’s brightness and activity, allowing for a more complete analysis of the phenomenon. The sublimation of dry ice (carbon dioxide) on its surface was identified as the main trigger for the release of vapor and dust, which became visible at specific wavelengths.
The mechanism behind the eruptions
Unlike terrestrial volcanoes, cryovolcanoes are phenomena that occur on icy celestial bodies. In the case of 3I/ATLAS, the mechanism is particularly unique, as it does not appear to be driven by internal heat, as in moons like Encélado of Saturno, but rather by a chemical corrosion process activated by solar radiation.
As the comet approached Sol, heating on its surface exceeded the threshold for sublimation of solid carbon dioxide. Esse process released the flow of oxidizing liquids that were trapped inside the celestial body, which, in turn, reacted chemically with metallic grains and sulfides present in its primitive composition.
This exothermic reaction generated internal pressure that culminated in the violent expulsion of gas and dust, forming the spiral jets that were observed. The absence of evidence of heat generated by significant radioactive decay reinforces the hypothesis that the comet’s activity is driven primarily by external factors.
Studies indicate that this aqueous corrosion mechanism explains the sudden and significant increase in brightness of the comet when it reached the 378 million kilometer mark from Sol, a behavior that initially intrigued astronomers.
Chemical composition of the stellar visitor
Spectroscopic analysis of material ejected by comet 3I/ATLAS has revealed an extraordinarily primitive composition, providing valuable clues about the raw material of its stellar system of origin. The data indicates that the core is a complex mixture of ice and rock, containing elements such as iron, nickel and highly reactive sulfides. Essa composition is remarkably similar to that of meteorites known as CR-type carbonaceous chondrites, which are considered some of the oldest and most unchanged materials in our Sistema Solar, often found in Antártida. The abundant presence of carbon dioxide, detected by Telescópio Espacial James Webb, along with traces of water ice and carbonyl sulfide, reinforces the primitive nature of the object. Além Furthermore, the detection of atomic nickel vapor suggests the existence of a metallic core that has been preserved for billions of years, possibly since before the formation of our own Sol, with an estimated age of between 7 and 14 billion years.
PRE-PERIHELION STUDY OF #COMET #3IATLAS with our findings about its spectroscopic similarity with CR carbonaceous chondrites. Manuscript submitted for publication in which we propose it is a #TNO-like body experiencing #cryovolcanism
Now in Cornell Univ. @arxiv repository:
➡️ arxiv.org/abs/2511.19112—Prof. Josep M. Trigo-Rodríguez (@joseptrigo.bsky.social) November 25, 2025 at 11:28
Hyperbolic origin and trajectory
The trajectory of comet 3I/ATLAS confirms that it is a true star traveler. Ele entered our Sistema Solar from the direction of the constellation of Sagitário, a region close to the center of Via Láctea. Sua excessive speed is the main evidence that it does not belong in our system, as it is too fast to be captured by the gravity of Sol.
Analysis of its orbital dynamics suggests that the comet may have originated in the thick disk of our galaxy, a region populated by older stars. If this hypothesis is confirmed, 3I/ATLAS would be one of the oldest objects ever studied directly by astronomers.
Measurements taken by Telescópio Espacial Hubble helped refine estimates of its size, which varies between 440 meters and 5.6 kilometers in diameter. Considerando a body about 1 kilometer in diameter, its estimated mass exceeds the mark of 600 million metric tons.
Contributions from other space missions
The passage of 3I/ATLAS through our system motivated a global observation campaign coordinated by Nasa, involving multiple missions and telescopes. Sondas orbiting Marte, like Perseverance and MAVEN, were used to capture images of its vast gaseous coma from a unique vantage point in space.
Mars Reconnaissance Orbiter played a crucial role in October 2025 in refining the comet’s trajectory, reducing the uncertainties of its orbit by a factor of ten. Esses accurate data was essential for pinpointing other telescopes, including the powerful James Webb, which detected the strong signature of carbon dioxide in its coma.
A time capsule from another solar system
Interstellar objects like 3I/ATLAS are of immense scientific value because they function as true time capsules. Eles carry with them the chemistry and conditions of their home star systems, materials that have been preserved in the cold deep of space for billions of years.
Analysis of its composition helps scientists better understand planetary formation processes in other parts of the galaxy. Além Furthermore, studying comets like this one can provide insights into how volatiles such as water and carbon compounds are distributed throughout the galaxy, a process that may be fundamental to the origin of life.
Visibility and approach to Terra
Comet 3I/ATLAS will make its closest approach to our planet on December 19, 2025, when it will pass at a safe distance of 270 million kilometers. Nesse period, it will be an accessible target for amateur astronomers equipped with medium-sized telescopes, who will be able to observe the glow of the interstellar visitor as it continues its long journey back into deep space, with its definitive departure from Sistema Solar expected in early 2026.
Future of interstellar research
Discoveries made from 3I/ATLAS observations are already driving new proposals for the development of space missions dedicated to intercepting future interstellar visitors. The possibility of closely studying an object with such a rare and primitive metallic composition offers an unprecedented opportunity to test theories about the accretion of matter into alien protoplanetary disks. Astrônomos also highlight the importance of continuing to monitor the sky to detect these objects, not only for their scientific value, but also to mitigate any potential risk, however rare, of a future impact.
