The third interstellar object confirmed to visit Sistema Solar passed through the closest point to Sol. Observações carried out in January 2026 revealed changes in the chemical composition of its coma. Comet 3I/ATLAS, also known as C/2025 N1 (ATLAS), was discovered in July 2025 by the ATLAS system. Ele follows a hyperbolic trajectory and is not gravitationally bound to Sol.
Astronomers used Telescópio Subaru, located at Mauna Kea, at Havaí, to capture detailed images of the object’s coma just after perihelion. The equipment has a main mirror with an effective diameter of 8.2 meters. The images combine data from three filters: V (550 nm), R (660 nm) and I (805 nm). Isso allowed analyzing the proportion of gases released.
Post-perihelium observations detect chemical variation
Telescópio Subaru performed the measurements on January 7, 2026. The results indicate that the ratio of CO₂ to H₂O in gases released after perihelion was significantly lower than that recorded by space observatories before Sol’s closest pass. Essa difference points to changes in core activity as the object warmed.
The sublimation of ice exposed deeper layers of the core. Camadas External release more volatile compounds first. With the increase in solar temperature, the internal material, with different proportions, began to dominate the release of gases. Esse process confirms that the core structure is not uniform.
Comet 3I/ATLAS approaches Sol at a distance of about 1.36 AU at perihelion, which occurred in October 2025. Ele passed at safe distances from planets such as Marte, Vênus and Terra. The trajectory Hyperbolic guarantees that the object will continue its path out of Sistema Solar after the visit.
Core structure explains the observed changes
The variation in composition reflects differences between the surface and inner layers of the core. Materiais more volatile compounds, such as certain compounds rich in carbon and oxygen, sublime at lower temperatures. As solar heating removes the outer layers, the exposed interior releases gases with a different ratio of CO₂ to water.
This characteristic helps to understand processes that occur in cometary nuclei of interstellar origin. Comparações with comets from Sistema Solar show that objects formed in other stellar systems can have different compositions. The data contributes to the study of planet formation in young systems around other stars.
- Combined observations from three filters allowed mapping of the coma at different wavelengths
- Analysis focused on the proportion of CO₂ to H₂O in the gases released
- Results indicate layered structure in the comet nucleus
- Change occurred due to progressive heating during solar approach
- Data will be published soon in the journal The Astronomical Journal
Context of interstellar objects observed so far
3I/ATLAS represents the third object confirmed as interstellar to cross Sistema Solar. The previous ones were 1I/’Oumuamua, in 2017, and 2I/Borisov, in 2019. Diferente of the first two, this object behaves like an active comet, releasing dust and gases as it approaches Sol.
Astronomers monitored 3I/ATLAS with several ground- and space-based instruments for months. The initial discovery took place on July 1, 2025, at Chile. The speed and hyperbolic trajectory quickly confirmed its origin outside of Sistema Solar. The object poses no risk of impact with Terra or other planets.
The new observations of Subaru add details about the physical and chemical evolution during its passage through perihelion. Elas reinforce the importance of studying these rare visitors to compare primordial matter from different regions of the galaxy. The comet will continue to move away and, in a few thousand years, will completely leave the area around Sistema Solar.
Scientific importance of coma analysis
The study of the coma allows access to information about the interior of the nucleus without direct contact. The change in the proportion of gases reflects how solar heating affects different materials over time. Isso offers clues about the chemical conditions in the comet’s home star system.
Researchers highlight that objects like 3I/ATLAS carry material formed billions of years ago, possibly in older regions of Via Láctea. Comparison with local comets helps map differences in planetary formation processes. The results from Subaru contribute to models that describe the evolution of cometary nuclei under stellar influence.
The work involved combining data from multiple filters for greater accuracy in component identification. The publication scheduled for next week on The Astronomical Journal should provide more technical details about the measurements and their implications.
