Comet 3I/Atlas, detected on July 1, 2025 by the Atlas system in Chile, crosses the Solar System at more than 30 km/s on a hyperbolic trajectory. Identified as the third confirmed interstellar object, it does not belong to our star system and offers clues about the formation of distant systems. Its minimum approach to Earth, 270 million kilometers, presents no risks. Astronomers use telescopes like the James Webb to study its unique chemical composition.
The comet, with a nucleus of around 1 km in diameter, displays a high concentration of carbon dioxide ice (CO₂), as well as water vapor and carbon monoxide. These characteristics differ from local comets, suggesting formation in extremely low temperature environments. Observations indicate that the object was ejected from another star system billions of years ago. The perihelion, the closest point to the Sun, is predicted for the next few weeks, at 210 million kilometers.
- High concentration of frozen CO₂ on the surface.
- Presence of water vapor and carbon monoxide in smaller quantities.
- Hyperbolic trajectory confirms interstellar origin.
- Cometary activity increases closer to the Sun.
Detection in the Atacama Desert
The Atlas system, located in Chile, identified the comet during routine observations. Its orbit, not gravitationally bound to the Sun, was confirmed by escape velocity calculations.
Unique chemical composition
Spectroscopic analyzes show a predominance of frozen CO₂, indicating formation at temperatures below -100°C. This feature suggests origins in the outer regions of another star system.
Water vapor appears in smaller quantities compared to typical solar comets. Carbon monoxide reinforces the 3I/Atlas’ volatile profile.
The nucleus, estimated at 1 km, releases gases that form a visible coma. Activity increases as it approaches the Sun.
Intensive global monitoring
Telescopes in Hawaii and Spain track daily variations of the comet. The James Webb captures infrared images to map the distribution of materials.
Data collected feed models on chemical evolution in protoplanetary disks. More than 50 institutions in 20 countries collaborate on the study.
The comet’s sublimation rate increases 20% for every million kilometers closer to the Sun. Peak brightness, at magnitude 10, is expected in the coming weeks.
Comparison with other interstellar objects
Unlike 1I/Oumuamua, which did not exhibit cometary activity, 3I/Atlas has a distinct gaseous tail. Compared to 2I/Borisov, it has a higher CO₂ content.
These differences highlight the diversity in interstellar formation processes. Each object provides unique data about conditions in distant systems.
Future trajectory confirmed
After perihelion, the comet will accelerate out of the Solar System, reaching speeds above 40 km/s. The passage through Mars’ orbit is scheduled for December 2025.
Detailed technical notes
High-resolution instruments detect specific emissions from molecules in 3I/Atlas. Spectra show the absence of fine dust, common in local comets, reinforcing their external origin.
