The interstellar comet 3I/ATLAS, the third confirmed object coming from outside Sistema Solar, reached its closest approach to Terra on December 19, 2025, passing at a safe distance of approximately 270 million kilometers. Essa passage allowed detailed observations by space telescopes, revealing never-before-detected X-ray emissions from interstellar visitors. Descoberto in July 2025 by the ATLAS system in Chile, the comet follows a hyperbolic trajectory and is now definitively moving away from Sistema Solar.
Astronomers have monitored the object intensively since its detection, using multiple missions to capture data at different wavelengths. The relative proximity to Terra, although still distant, facilitated the collection of information about its composition and behavior. The comet did not pose a risk of collision at any point in its trajectory.
- Perihelion, the closest point to Sol, occurred in October 2025, around 210 million kilometers away.
- After this phase, 3I/ATLAS headed toward Earth’s approach, exhibiting typical cometary activity.
- Observations confirmed the presence of a coma and tail, with the release of gases and dust.
Discovery and orbital trajectory
Comet 3I/ATLAS was identified on July 1, 2025 by telescopes from the ATLAS project, funded by NASA and located at Chile. Initial Análises of the orbit quickly indicated its interstellar origin, due to the eccentricity greater than 1 and high speed. Pré-discoveries in archived images date back to June 2025, allowing us to refine orbital calculations from scratch.
Its hyperbolic trajectory confirms that the object is not gravitationally bound to Sol, differentiating it from comets native to Sistema Solar. 3I/ATLAS entered from the direction of the constellation Sagitário, passed close to Marte in October and reached perihelion before approaching Terra.
Observations at multiple wavelengths
Ground- and space-based telescopes captured detailed images of the comet throughout its passage. Telescópio Espacial Hubble recorded variations in its morphology, showing an elongated teardrop-shaped coma. Missões as JUICE and PUNCH obtained unexpected views, revealing structures of dust and gases.
Recent images indicate that the comet developed a greenish glow after perihelion, due to the sublimation of volatiles. Observações optics showed ion tailing and antitailing, common phenomena in active comets but valuable in an object from another star.
X-ray emissions detected
For the first time on an interstellar comet, missions captured X-ray emissions. The XRISM mission, led by JAXA with participation from NASA and ESA, observed the object for 17 hours in late November 2025. The data revealed a faint glow in X-rays extending up to 400,000 kilometers around the nucleus.
Agência Espacial Europeia complemented the XMM-Newton observatory, which monitored the comet for around 20 hours on December 3, 2025. The most sensitive camera recorded a characteristic red glow, resulting from the interaction between cometary gases and the solar wind.
These emissions arise from interactions between charged Sol particles and sublimated materials such as water vapor, carbon monoxide and carbon dioxide. Assinaturas spectra indicated the presence of carbon, oxygen, nitrogen and possibly diatomic hydrogen near the nucleus.
X-ray observations provide complementary data to infrared and radio analyses, helping to map the chemical composition of the comet.
Chemical composition revealed
Combined analyzes suggest that 3I/ATLAS has volatiles similar to solar comets, but with atypical proportions. Detectaram excess of certain elements, such as nickel in initial observations, and richness in carbon dioxide. Essas variations indicate formation in a distant protoplanetary disk, possibly older than Sistema Solar.
The estimated core varies between 440 meters and 5.6 kilometers in diameter, surrounded by an extensive coma. Dados X-rays add information about light elements that are difficult to detect at other wavelengths.
Public viewing opportunities
Although not visible to the naked eye, the comet could be observed with amateur telescopes during December 2025. Projetos and Virtual Telescope transmitted live images during closest approach.
The brightness gradually decreased after December 19, but the object remained accessible for a few additional months. Entusiastas in places with low light pollution recorded detailed photos of the tail and coma.
Comparison with previous interstellar objects
3I/ATLAS differs from its predecessors ‘Oumuamua, from 2017, and Borisov, from 2019.
This passage represents the third opportunity to study material formed in another star system. Cada object provides clues about planetary formation processes in varied cosmic environments.
The comet is now heading to the outer regions, with a distant passage through Júpiter scheduled for 2026. Sua hyperbolic speed guarantees permanent exit from Sistema Solar in the next decade.
