Interstellar comet 3I/ATLAS mobilizes space agencies with unusual and mysterious radio emission

The passage of a rare visitor from outside our Sistema Solar, comet 3I/ATLAS, generated an intense global scientific mobilization in 2025. The object, quickly classified as interstellar due to its unique trajectory, triggered intensive monitoring protocols from NASA and other space agencies after the detection of a continuous and unusual radio emission.

Analysis of the signal, although later confirmed to be of natural origin, warranted in-depth investigation due to its remarkable intensity and regularity. The international collaboration, which involved Agência Espacial Europeia (ESA), employed a global network of observatories to track the comet and collect as much data as possible during its brief visit to our system.

As the third interstellar object ever recorded by science, the passage of 3I/ATLAS represented a unique opportunity to study materials from another stellar system. Scientific teams focused on unlocking secrets about its chemical composition and the environment from which it was ejected millions of years ago, before continuing its journey into deep space.

The discovery and journey of the cosmic traveler

Comet 3I/ATLAS was detected for the first time on July 1, 2025. The identification occurred thanks to the ATLAS astronomical survey system (Asteroid Terrestrial-impact

Immediately after the discovery, astronomers from several institutions calculated its orbit and speed. The celestial body was traveling at approximately 100,000 km/h relative to Sol, following a hyperbolic trajectory. Essa open curve, which does not close into an orbit, served as definitive confirmation of its extrasolar origin, indicating that it was just passing through.

Preliminary analyses, coordinated by teams from Universidade, Havaí and ESA, indicated that 3I/ATLAS was a fragment composed of rock and ice. The most accepted theory is that it was expelled from its original star system by a gravitational event of great magnitude, such as the interaction with a giant planet or the close passage of another star.

Estimates of the size of its core have varied considerably, ranging between 320 meters and 5.6 kilometers in diameter. The nucleus was surrounded by a coma, a cloud of gas and dust formed by the sublimation of ice under the heat of Sol, a behavior typical of active comets and which provided the first clues about its composition.

The mystery of the 1.6 GHz frequency

The most fascinating aspect of comet 3I/ATLAS was revealed on October 24, 2025, when the MeerKAT radio telescope, on África of Sul, captured a consistent radio emission coming from the object. The signal was recorded at a frequency of 1.6 GHz, a band that corresponds to one of the emission lines of hydroxyl molecules (OH), a common byproduct of the breakdown of water molecules (H2O) by solar radiation in active comets. Embora the origin of the signal was natural, its strength and regularity were considered remarkable, ruling out any possibility of terrestrial or artificial interference. Essa emission not only validated 3I/ATLAS’s classification as an active comet, but also offered scientists an innovative tool to measure the rate of sublimation of water on its surface, providing crucial data about its internal composition and its reaction to our Sistema Solar’s environment.

Planetary Security Protocols in Action

Despite confirmation of the natural origin of the signal, the combination of an interstellar trajectory with atypical behavior led to the activation of NASA’s Escritório of Coordenação of Defesa Planetária (PDCO) protocols. The measure, although standard for newly discovered objects with unusual orbits, reflects the seriousness with which space agencies treat any potential threat from space, regardless of its origin.

The PDCO’s primary role is to oversee efforts to detect, track, and characterize nearby objects. The passage of 3I/ATLAS served as a valuable exercise to test and improve global response systems and real-time data analysis. The world’s most advanced observatories, such as Very Large Telescope (VLT) at Chile and Telescópio Espacial James Webb, have dedicated observing time to analyze the chemical spectrum of the comet’s coma and obtain maximum information.

Safe trajectory and goodbye to the solar system

Detailed orbital calculations, carried out independently by NASA and ESA, confirmed that comet 3I/ATLAS posed no threat of collision with Terra or other planets in Sistema Solar. The accurate analysis of his trajectory was essential to reassure the public and allow the scientific community to focus exclusively on his research aspects.

Its closest approach to our planet occurred on December 19, 2025, at a safe distance of 270 million kilometers, which is equivalent to almost double the average distance between Terra and Sol. Essa distance ensured that its passage would not have any gravitational effect or other impact on our planet.

The comet’s path is a classic example of an interstellar trajectory. Após reached perihelion, its closest point to

How 3I/ATLAS compares to other interstellar visitors

3I/ATLAS has joined a select list of confirmed interstellar objects, which includes 1I/’Oumuamua, detected in 2017, and 2I/Borisov, observed in 2019. Cada one of these visitors offers distinct pieces to the puzzle about the formation of other planetary systems and the diversity of celestial bodies in Via Láctea.

Unlike ‘Oumuamua, which had an elongated shape and did not display a visible coma, 3I/ATLAS demonstrated clear cometary activity, more similar to 2I/Borisov. However, the intensity of its radio signal differentiated it from both, suggesting a unique composition or internal structure, which continues to be the subject of study and debate among experts.

The importance of continuous surveillance of the skies

Events such as the passage of 3I/ATLAS reinforce the importance of continuous monitoring systems such as ATLAS. Esses programs are key to detecting unexpected visitors in advance, enabling precise calculation of their orbits to ensure planetary safety and seize rare scientific opportunities, which could provide unprecedented insights into the universe beyond our Sistema Solar.

The scientific legacy and future observations

Even as it moves away, monitoring 3I/ATLAS remains a priority for several research groups. Current observations seek to track variations in the composition of its coma and the reflectivity of its core as it moves into colder, more distant regions of space.

The data collected will help understand how the heat of Sol affected its internal structure during its passage through our system. Essas information is valuable for understanding the resilience and evolution of celestial bodies in stellar environments different from their places of origin, enriching our knowledge about the formation and dynamics of planetary systems throughout the galaxy.