Interstellar comet 3I/ATLAS and its unusual radio signal have mobilized space agencies around the world

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

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 passage through our system.

As the third interstellar object ever recorded by science, the 3I/ATLAS visit represented a unique opportunity to study materials from another star 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 origin and journey of the cosmic visitor

Comet 3I/ATLAS was first detected on July 1, 2025, thanks to the astronomical survey system ATLAS (Asteroid Terrestrial-impact Last Alert System), operated from the observatory at Río Hurtado, at Chile. Imediatamente after its discovery, astronomers around the world rushed to calculate 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 the definitive confirmation of its extrasolar origin. Preliminary Análises, 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 home star system by a gravitational event of great magnitude, such as the interaction with a giant planet. Estimates of the size of its nucleus varied considerably, between 320 meters and 5.6 kilometers in diameter, and it was surrounded by a coma, a cloud of gas and dust formed by the sublimation of ice under the heat of Sol, behavior typical of active comets.

Details of the enigmatic radio broadcast

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.

This emission not only validated 3I/ATLAS’s classification as an active comet, but also offered scientists an innovative tool for measuring the rate of water sublimation on its surface. Isso provided crucial data about its internal composition and its reaction to our solar system’s environment. The detailed analysis made it possible to estimate the amount of material that the comet was losing as it approached Sol, offering valuable clues about the constitution of celestial bodies formed around other stars.

The response from global space agencies

Despite confirmation of the signal’s natural origin, the combination of an interstellar trajectory with atypical behavior led NASA’s Escritório of Coordenação of Defesa Planetária (PDCO) to activate its monitoring protocols.

The PDCO’s primary role is to oversee efforts to detect, track, and characterize objects near Terra. 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.

International collaboration was key to ensuring continuous coverage of the object, allowing different teams around the globe to share discoveries and validate observations independently.

Safe trajectory through 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 the solar system.

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.

Comparison with other interstellar objects

3I/ATLAS joined a select list of confirmed interstellar objects, which includes 1I/’Oumuamua, detected in 2017, and 2I/Borisov, observed in 2019.

Each of these visitors offers distinct pieces to the puzzle about the formation of other planetary systems and the diversity of celestial bodies in the universe.

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.

The importance of celestial scanning systems

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, allowing accurate calculation of their orbits to ensure planetary safety and maximize scientific opportunities.

The scientific legacy of comet 3I/ATLAS

Even as it moves away, monitoring 3I/ATLAS has remained a priority for the scientific community. Observations continued to track variations in the composition of its coma and the reflectivity of its core as it returned to the cold of deep space.

The data collected will help understand how the heat of Sol affected its internal structure during its passage through our system, providing valuable information about the resilience and evolution of celestial bodies in stellar environments different from their original.