The interstellar comet 3I/ATLAS, the third object confirmed to originate outside our Sistema Solar, has shown a notable increase in brightness and a distinction in its hue. Recent Imagens, captured on November 26, 2025 by Telescópio Gemini North, located at Havaí, revealed that the celestial body displays a striking greenish color in its coma, which denotes a phase of intense activity after its closest passage to Sol, which occurred in October. Essa change in light emission offers scientists crucial data about the composition and behavior of objects from other stars.
The comet’s coma, a vast cloud of gases and dust that forms around the nucleus when it is heated by solar energy, now radiates a bright green glow. Este new appearance contrasts significantly with the reddish color that had been recorded in previous months, indicating the release of new molecules and volatile compounds as the comet’s icy nucleus sublimates under the influence of solar heat. Tais observations are vital to understanding the chemical processes that occur in interstellar comets.
3I/ATLAS’s closest approach to Terra is scheduled for December 19, 2025. The object will pass at a safe distance of approximately 270 million kilometers from our planet, offering a window of opportunity for in-depth observations without any risk of collision or impact.
Manifestation of greenish color
The characteristic green hue that now dominates the 3I/ATLAS coma is attributed primarily to the presence of diatomic carbon. Esta molecule, composed of two carbon atoms, has the ability to emit light in the green range of the electromagnetic spectrum when it is excited by the intense radiation emitted by Sol. It is a well-known astrophysical phenomenon and is frequently observed in comets that are activated by solar heat, with notable examples on other celestial bodies such as 12P/Pons-Brooks and C/2025 F2 (SWAN).
The color transition from reddish to greenish in the comet’s coma provides an important clue about the object’s internal structure. Essa visual change suggests that solar heat is penetrating deeper layers of the cometary nucleus, releasing different types of volatile compounds that were not active during initial observations. In August and September 2025, for example, Telescópio Gemini South had not detected the emission of this green light, which reinforces the evolutionary nature of the comet’s activity.
Intensified activity after perihelion
The activity of comet 3I/ATLAS experienced a notable increase after its perihelion, the closest passage to Sol, which occurred on October 29, 2025. At Neste point, the comet was at a distance of 1.4 astronomical units from the star, which intensified the heating of its nucleus. The ice present inside the comet began to sublimate directly into the gaseous state, a process that expels large amounts of dust and contributes to the formation of a more extensive and brighter coma.
The response of comets to solar heat is not always immediate. Muitos of them demonstrate delayed reactions, with the possibility of material outbursts and gas explosions even after they have started their trajectory away from the Sol. In the context of 3I/ATLAS, astronomers maintain continuous monitoring to check whether new eruptive events, known as “outbursts”, may occur during its phase of maximum approach to Terra, which could alter its brightness and appearance.
Composite images, obtained using blue, green, orange and red filters, have been essential in highlighting the nebulous nature of the coma and the incipient formation of the comet’s tail. The telescope’s tracking system allows the comet’s motion to be isolated, making background stars appear as colored dashes. Essas variations in appearance provide crucial information about the composition and dynamics of 3I/ATLAS, one of the oldest and largest interstellar visitors ever identified.
Interstellar trajectory and nature
Discovered on July 1, 2025 by the ATLAS system (Asteroid Terrestrial-impact Last Alert System) operating at Chile, 3I/ATLAS was quickly identified by its hyperbolic orbit. Esta orbital characteristic is the main evidence that confirms its external origin to Sistema Solar, differentiating it from comets that formed in our own cosmic neighborhood. Sua travel speed, exceeding 200 thousand kilometers per hour, guarantees that it will not return to our region of space after its passage.
Current estimates suggest that the comet’s nucleus may vary in diameter, ranging from 440 meters to 5.6 kilometers. Cometary activity from 3I/ATLAS was first detected in May 2025, when the object was still a considerable distance of 6.4 astronomical units from Sol. Analysis of its trajectory and composition indicates the possibility that it formed in the thick disk of Via Láctea, a region rich in primordial material.
3I/ATLAS distinguishes itself from other previously observed interstellar objects, such as ‘Oumuamua and Borisov. Unlike its predecessors, this comet displays a wide, well-defined coma, as well as dust and ion tails that extend for millions of kilometers. The presence of jets of material oriented toward Sol is also a notable feature, offering researchers a unique opportunity to study the evolution of an active interstellar comet.
Extensive recording by global observatories
The 3I/ATLAS observation mobilized a vast network of astronomical instruments around the world, with the aim of collecting as much data as possible about this unique visitor. Telescópio Espacial Hubble, for example, recorded stunning details of the comet’s coma and tails on November 30, 2025, providing high-resolution images that complement ground-based observations. Além In addition, the JUICE probe from Agência Espacial Europeia (ESA) also contributed its own records, expanding the scope of the research.
Observations were not limited to the visible spectrum; X-ray emissions were detected, associated with the comet’s interaction with the solar wind, providing data on the ionization processes. Mesmo amateur astronomers, using modest equipment, managed to capture images that demonstrate the vast extent of the coma, which can reach millions of kilometers. Campanhas observations coordinated by agencies such as NASA and ESA, in collaboration with several ground-based observatories, are scheduled to continue until 2026, ensuring comprehensive monitoring of the comet. 3I/ATLAS remains visible in the morning sky, with an apparent magnitude of around 12, requiring the use of telescopes for its precise location in constellations such as Leão.
Identification of chemical composition
Spectroscopic analyzes carried out at 3I/ATLAS revealed a rich and complex chemical composition, providing clues about its formation environment. Carbon dioxide appears as a dominant component, but other compounds such as methanol, hydrogen cyanide and ionized nickel have also been detected at high levels. The presence of these elements suggests that the comet originated in extremely cold and distant environments, possibly in the outer regions of its home star system.
While the detection of water and other volatiles reinforces similarities to comets that formed in our own Sistema Solar, the identification of unique chemical traits points to significant differences in their stellar origin. Dados obtained by the Atacama Large Millimeter/submillimeter Array (ALMA) and the Very Large Telescope (VLT) complement the optical images, offering a more complete view of the comet’s molecular structure. Essas information is crucial to understanding how chemical elements are distributed in different planetary systems.
Safe approach to Terra
The passage of 3I/ATLAS on December 19, 2025, when it will be 270 million kilometers from Terra, represents a considerable distance, equivalent to almost twice the average separation between Terra and Sol. Essa safety margin ensures that there is no risk of collision or impact with our planet. The approach provides a valuable opportunity for the scientific community to perform detailed observations before the comet follows its trajectory and moves permanently away from our stellar neighborhood.
The comet’s brightness may vary, especially if late bursts of material occur, which is a common phenomenon in comets. Após the month of December, 3I/ATLAS will continue its journey towards the outer regions of Sistema Solar, gradually becoming invisible to ground-based telescopes. The in-depth study of 3I/ATLAS is fundamental to expanding our understanding of planetary formation processes in ancient and distant star systems, contributing to astrophysics and cosmology.