Scientists have recorded an extraordinary phenomenon in the third interstellar visitor ever detected in our Sistema Solar. Novas high-resolution images of comet 3I/ATLAS, captured by Observatório Montsec, on Catalunha, Espanha, revealed clear evidence of cryovolcanic eruptions, jets of gas and dust expelled from its icy surface. Este event offers unprecedented insight into the composition of celestial bodies formed in other star systems.
The observations were carried out with Telescópio Joan Oró as the comet made its approach to Sol, in October 2025. Solar heating intensified activity on the object’s surface, allowing astronomers to study in detail the processes that govern these primitive bodies. The discovery reinforces the theory that 3I/ATLAS is rich in volatile ices and materials that date back to the formation of its home system.
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’s hyperbolic trajectory, which does not form a closed orbit around Sol, is confirmation of its interstellar origin, making it a rare and valuable sample of a distant planetary environment.
Initial observations at perihelion
Although monitoring of the comet began shortly after its discovery, it was in October 2025 that its activity increased dramatically. Perihelion, the point of its orbit closest to Sol, occurred on October 29 of that year, at a distance of 1.36 astronomical units (approximately 203 million kilometers) from our star.
The images obtained by Telescópio Joan Oró were crucial, as they captured the jets of matter with unprecedented resolution, revealing spiral structures in the expelled dust and gas. Esses data was supplemented by a network of regional observatories on Espanha, which helped build a more complete picture of the comet’s behavior. The process is driven by the sublimation of dry ice (carbon dioxide), which turns directly into gas, releasing dust and other volatiles trapped in the comet’s nucleus.
Composition and similarities with Sistema Solar
Detailed analyzes of the light reflected by the comet indicate that 3I/ATLAS shares characteristics with trans-Neptunian objects (TNOs) from our own Sistema Solar, such as the dwarf planets and other icy bodies that inhabit Cinturão of Kuiper. Essa similarity suggests that planetary formation processes in other star systems may not be so different from those that occurred here.
The composition of the ejecta includes elements such as iron, nickel and reactive sulfides. Essa’s chemical signature is comparable to that of CR-type carbonaceous chondritic meteorites, which are some of the most primitive materials known, remnants of the nebula that gave rise to our Sol and the planets. Essas space rocks are rich in carbon and volatile compounds.
Solar heating appears to have triggered chemical reactions inside the comet, releasing gases such as carbon monoxide and cyanide. The detection of atomic nickel vapor in its coma (the gaseous atmosphere around the nucleus) reinforces the hypothesis that the celestial body has a metallic core preserved beneath its ice crust.
Mechanism of cryovolcanic eruptions
Cryovolcanoes, or ice volcanoes, are phenomena that occur on frozen celestial bodies, where internal heat melts underground ice, expelling steam, liquids and dust to the surface. However, the mechanism observed in 3I/ATLAS is distinct in that it does not appear to be driven by significant internal heat, such as that generated by radioactive decay or tidal forces.
In the case of this interstellar comet, the engine of the process is external: solar radiation. As the comet approached Sol, its surface temperature exceeded the threshold for sublimation of solid carbon dioxide. Esse process allowed oxidizing liquids, trapped inside, to flow and come into contact with pristine metallic grains.
The resulting chemical reaction between the oxidants and metals generated the energy needed to expel the high-speed jets of gas and dust. Foram these emissions formed the spiral structures observed by telescopes, also explaining the sudden and significant increase in brightness of the comet when it reached the 378 million kilometer mark from Sol.
This form of cryovolcanism, dependent on chemical corrosion activated by external heat, differentiates 3I/ATLAS from other bodies with known volcanic activity, such as the moon Encélado of Saturno or the dwarf planet Plutão, whose processes are mostly driven by internal heat sources.
Interstellar trajectory and origins
Comet 3I/ATLAS 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 definitive proof that it is not gravitationally bound to Sol and, after its passage, it will continue its journey through interstellar space. Orbital dynamics suggest that its origin may be in our galaxy’s thick disk, a region that contains older stars, indicating that the comet may be billions of years old.
Observations carried out by Telescópio Espacial Hubble helped determine its size, estimated at between 440 meters and 5.6 kilometers in diameter. Considerando a body measuring about 1 kilometer, its mass would exceed 600 million metric tons. The research team, led by Professor Josep M. Trigo-Rodríguez, submitted a pre-perihelion study proposing that the object is a TNO-like body that is experiencing cryovolcanism.
Observations from multiple missions
The 3I/ATLAS study involved a campaign coordinated by NASA, using several instruments and space probes. Telescópio Espacial James Webb detected an abundance of carbon dioxide in its coma, with traces of water ice and carbonyl sulfide. Sondas orbiting Marte, like Perseverance and MAVEN, also captured images of the comet’s gaseous coma, taking advantage of their unique vantage point on Sistema Solar.
Mars Reconnaissance Orbiter (MRO) played a key role in refining the comet’s trajectory in October, reducing uncertainties in its position by a factor of ten. Essa precision was essential so that other observatories, both on Terra and in space, could point their instruments at the target accurately and maximize scientific data collection during their brief visit.
Scientific importance of the visitor
Interstellar objects like 3I/ATLAS function as true time capsules, preserving the chemistry and physical conditions of distant stellar systems. Sua direct analysis allows scientists to better understand planet formation processes elsewhere in the galaxy, as well as investigating the role comets may play in delivering volatile compounds such as water and organic molecules to rocky planets, a potentially crucial step towards the origin of life. With its departure from Sistema Solar scheduled for 2026, observations remain a priority. The detection of radio waves at a frequency of 1420 MHz, although of natural origin, helped to rule out speculation about an artificial origin. The comet will make its closest approach to Terra on December 19, 2025, at a safe distance of 270 million kilometers, when it will be visible with amateur telescopes.
Imaging and spectroscopic data
Photometry, a technique that measures light intensity, was used to track the comet’s increase in brightness before it reached perihelion. The luminosity peaks were recorded mainly at infrared wavelengths, which is consistent with thermal emission from dust and gas expelled from its surface.
Detailed comparisons with meteorite samples collected at Antártida confirmed the spectroscopic similarities of 3I/ATLAS with CR-type chondrites, which are rich in carbon. Esses meteorites are considered fossils of the early solar nebula, which makes the composition of the interstellar comet even more intriguing to scientists.
Future of interstellar research
The discoveries made from the 3I/ATLAS study are driving new proposals for the development of interceptor space missions. The idea is that, in the future, a probe could be launched quickly to find one of these interstellar visitors and analyze it up close, collecting data that is impossible to obtain from Terra.
The rare metallic composition suggested by the observations indicates distinct accretion processes in the protoplanetary disks where these objects form. Finally, astronomers emphasize that continually monitoring the sky for these visitors is critical not only for science but also for planetary defense in order to mitigate potential risks, even though the likelihood of an impact is extremely low.