Interstellar comet 3I/ATLAS intrigued scientists with unique radio emission during its rare visit

The passage of a rare visitor from outside our Sistema Solar, comet 3I/ATLAS, generated an intense global scientific mobilization throughout 2025. Identificado at the beginning of the year, 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 as being 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 focused on uncovering secrets about its chemical composition and the environment from which it was ejected millions of years ago, before continuing its journey into 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 astronomical survey system ATLAS (Asteroid Terrestrial-impact

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 open curve, which does not close in 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 he was expelled from his home star system by a gravitational event of great magnitude, such as the interaction with a giant planet, being launched on a solitary journey through interstellar 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 typical behavior of active comets and a clear sign of their dynamic nature.

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 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 natural origin of the signal, the combination of an interstellar trajectory and atypical behavior led NASA’s Escritório of Coordenação of Defesa Planetária (PDCO) to intensify monitoring of the object.

The PDCO’s primary role is to oversee efforts to detect, track, and characterize objects near Terra that may pose a threat. The passage of 3I/ATLAS served as a valuable exercise to test and improve global response systems and real-time data analysis, preparing agencies for unexpected future visitors.

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 about its composition.

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 trajectory, although passing through our cosmic neighborhood, was well defined and presented no direct threats, allowing the focus to remain purely scientific.

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. When Após reached perihelion, its closest point to Sol, our star’s gravity acted like a catapult, accelerating it on its journey back into deep space, from where it will never return.

Comparisons with other interstellar travelers

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.

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 that is still being studied.

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 essential for detecting unexpected visitors in advance, allowing them to accurately calculate their orbits to ensure planetary safety and plan observation missions.

Observations and scientific focus

Even with the comet already moving away, monitoring 3I/ATLAS continues to be a priority for astronomers. Current observations seek to track variations in the composition of its tail and the reflectivity of its core as it moves into colder regions of 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 place of origin.