An in-depth analysis of the interstellar object 3I/ATLAS, the third visitor from outside our Sistema Solar already identified, ruled out the presence of artificial radio emissions, reinforcing its classification as a comet of natural origin. The scan was conducted in December 2025 by an international team from the Breakthrough Listen project, which used the powerful Telescópio Green Bank to monitor the object during its closest approach to Terra. The investigation, which searched for technosignatures across a wide spectrum of frequencies, did not find any evidence of technology, ending initial speculation and aligning the characteristics of 3I/ATLAS with astrophysical processes known and expected for celestial bodies of this nature, consolidating the understanding of their composition and behavior.
Discovered on July 1, 2025, 3I/ATLAS was quickly identified as an interstellar object due to its hyperbolic trajectory and high speed, which prevent it from being captured by the gravity of Sol. Sua passage offered a rare opportunity for scientists to study material from another star system.
Data collected by multiple observatories around the world, including Telescópio Espacial Hubble, corroborate the radio scan findings. Visual and spectroscopic observations revealed a bright coma, composed of gas and dust, and an icy nucleus, typical features of active comets.
Details of the discovery and the unusual trajectory
The identification of 3I/ATLAS was carried out by the astronomical survey system ATLAS (Asteroid Terrestrial-impact Last Alert System), located at Chile and funded by NASA. The object was detected as a fast-moving point of light, and subsequent orbital calculations confirmed its origin outside our Sistema Solar. Movendo is at a speed greater than 30 kilometers per second compared to Sol, its trajectory is classified as hyperbolic, which means that it is just passing through and will continue its journey through interstellar space after crossing our cosmic neighborhood. The comet reached its perihelion, the closest point to Sol, in October 2025, and on December 19 of the same year, it made its closest approach to Terra, passing at a safe distance of approximately 167 million kilometers, allowing a privileged observation window for terrestrial instruments.
The search for technological signals by Breakthrough Listen
The Breakthrough Listen project, one of the most ambitious initiatives in the search for extraterrestrial intelligence (SETI), has mobilized its resources to investigate 3I/ATLAS. On December 18, 2025, one day before closest approach, the team directed Telescópio Green Bank, in Virgínia Ocidental, toward the comet. Este instrument, which is the world’s largest fully steerable single-dish radio telescope, performed a thorough scan across a wide range of frequencies, covering 1 to 12 GHz. The main objective was to detect any narrowband radio signals that could not be explained by natural phenomena, so-called technosignatures, which could indicate the presence of alien technology, such as a probe or transmitter on board the object.
After hours of observation and rigorous analysis of the data collected, the Breakthrough Listen team found no localized artificial emission from 3I/ATLAS. Todos the recorded signals were identified as interference of terrestrial origin or known astronomical sources. The comet’s silence in the radio spectrum provided strong evidence against the hypothesis of a technological origin, aligning with all other observations pointing to a natural celestial body. The result, although negative in the search for intelligent life, was crucial for characterizing the object more accurately and understanding the nature of interstellar visitors.
Composition and cometary activity confirmed
Visual observations from 3I/ATLAS revealed a bright, expansive coma, the cloud of gas and dust that forms around a comet’s nucleus when it is heated by Sol. Essa activity is a clear indicator that the object is composed of volatile materials.
Detailed spectroscopic analyzes indicated that the core’s composition is dominated by carbon dioxide ice and water, which explains its prolonged activity even at great distances from the Sol. Essa composition differentiates it from other comets already studied.
Unlike the first interstellar visitor, ‘Oumuamua, the core of 3I/ATLAS does not have an extremely elongated shape. High-resolution Imagens shows a more symmetrical body, although considerably larger in size than the average comet in our system.
Jets of material being ejected from the surface of the nucleus have also been recorded by telescopes such as the Hubble and the Subaru. Esse behavior is consistent with the sublimation of ice, reinforcing the classification of 3I/ATLAS as an active and natural comet.
Differences and similarities with ‘Oumuamua and Borisov
The study of 3I/ATLAS is enriched by comparison with the only two previously confirmed interstellar objects. The first, 1I/’Oumuamua, detected in 2017, intrigued scientists for its peculiar shape, similar to a cigar, and for presenting a non-gravitational acceleration without a visible coma, which generated intense debate about its nature.
The second visitor, 2I/Borisov, identified in 2019, was much more familiar, displaying all the characteristics of a classic comet, with a well-defined coma and tail. Ele served as the first clear example of a comet coming from another star system and became an important reference.
3I/ATLAS appears to fall somewhere in between, combining a robust size, closer to ‘Oumuamua, with the evident cometary activity of 2I/Borisov. Essa diversity among the three known objects suggests that planetary systems across the galaxy can produce a vast array of celestial bodies.
The role of Green Bank Telescope in the investigation
The exceptional sensitivity of Telescópio Green Bank was fundamental to the search for technosignatures in 3I/ATLAS. Sua huge collection area allows it to detect extremely weak radio signals, which would be essential for picking up a possible transmission from a distant interstellar probe.
The telescope’s ability to operate across a wide range of frequencies simultaneously allowed the Breakthrough Listen team to conduct a comprehensive search in a short period, maximizing the chance of detection during the limited observation window of the comet’s passage.
Expert analysis and scientific debate
Astronomer Avi Loeb, of Universidade of Embora he maintains the importance of considering all hypotheses, recognizing that the accumulated evidence points strongly towards a natural explanation.
The consensus in the astronomical community is that 3I/ATLAS is a natural comet. The data collected by different teams and instruments are consistent with each other and paint a clear picture of an icy body ejected from its home star system and now traveling through Via Láctea.
Future of Interstellar Object Monitoring
The detection of three interstellar objects in just a few years, thanks to more advanced sky surveys, indicates that these visitors may be more common than previously thought. Future Projetos, such as the Observatório Vera C. Rubin, which will initiate the Legacy Survey of Space and
