Interstellar comet 3I/ATLAS emits unique radio signal and mobilizes global space observatories

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

Analysis of the signal, although later confirmed to be of natural origin, justified an in-depth investigation due to its intensity and regularity. The international collaboration, involving Agência Espacial Europeia (ESA), used 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 have focused on unlocking secrets about its chemical composition and the environment from which it was ejected millions of years ago, before continuing its journey through deep space.

Visitor discovery and characteristics

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 Last Alert System), operated from the Río Hurtado observatory, at Chile. The Esse system is designed to scan the night sky for moving objects, particularly asteroids that could pose a threat to the Terra, but its wide-field surveillance capabilities make it ideal for discovering unexpected visitors like this.

Soon after its discovery, astronomers around the world calculated its orbit and speed. The star was traveling at approximately 100,000 km/h in relation to Sol, following a hyperbolic trajectory. Essa’s open curve, which does not close into an orbit, served as definitive confirmation of its extrasolar origin, indicating that it possessed enough energy to escape the gravitational pull of Sol and return to interstellar space.

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 he was expelled from his home star system by a gravitational event of great magnitude, such as an interaction with a giant planet. Esse type of event can disrupt the orbits of comets in distant systems, launching them on long journeys through space.

Estimates of the size of its core 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. The presence of this coma was one of the factors that differentiated it from other previously observed interstellar visitors.

The enigmatic captured radio signal

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 intensity 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 for measuring 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 Activated

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

The PDCO’s primary role is to oversee efforts to detect, track, and characterize nearby Terra objects (NEOs). Although 3I/ATLAS was not a threat, its passage 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 analyzing the chemical spectrum of the comet’s coma and gaining as much information as possible during its brief stay.

Hyperbolic trajectory and impact risk

Detailed orbital calculations, carried out independently by NASA and ESA, confirmed that comet 3I/ATLAS posed no danger of collision with Terra or other planets in Sistema Solar.

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.

The comet’s path is a classic example of an interstellar trajectory. When Após reached perihelion, its closest point to Sol, our star’s gravity acted like a slingshot, accelerating it on its journey back into deep space, from where it will never return.

Comparisons with other interstellar travelers

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 in our galaxy.

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 set it apart from both, suggesting a unique composition or internal structure that still intrigues scientists.

The importance of continuous monitoring

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.

Observations and scientific focus

Even as it moves away, monitoring 3I/ATLAS remains a priority. Current observations seek to track variations in the composition of its coma and the reflectivity of its core.

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.