3I/Atlas, detected by Atlas in Chile, brings clues about the formation of stellar systems
Comet 3I/Atlas advances through the Solar System with a speed of more than 30 km/s and follows a hyperbolic trajectory. The object, the third confirmed interstellar, was identified on July 1, 2025 by the Atlas system in Chile. Its origin external to our stellar system allows studies of materials formed in distant environments.
Astronomers use telescopes like the James Webb to analyze its composition. The comet poses no risk to Earth, with a minimum approach of 270 million kilometers. Observations continue until perihelion, scheduled for the next few weeks at 210 million kilometers from the Sun.
- Elements detected include carbon dioxide ice in high concentration.
- Presence of water vapor and carbon monoxide differentiates it from local comets.
- Trajectory indicates ejection from another star system billions of years ago.
3I/ATLAS Is Not Behind the Sun.
— 3I/ATLAS (@3IAtlas_Anomaly) October 28, 2025
Astronomers were told the interstellar object would disappear behind the Sun during its Oct 29 perihelion. But new observations show that’s not true.
On Oct 25, the team recorded 3I/ATLAS visible beside the Sun — not hidden.
Position: RA 13h 38m… pic.twitter.com/cqRoIn8PGT
Initial detection
The Atlas system recorded the comet in routine observations in the Atacama Desert. Preliminary data showed an orbit not gravitationally bound to the Sun.
Calculations confirmed an escape velocity greater than that of the Solar System. International teams validated the classification as interstellar within a few days.
Chemical composition
Spectroscopic analyzes revealed a predominance of frozen CO₂ on the surface. This feature suggests formation at temperatures below -100°C in outer regions of another system.
Water vapor appears in smaller quantities than in typical solar comets. Carbon monoxide completes the observed volatile profile.
The core measures about 1 kilometer in diameter, according to estimates based on brightness. Cometary activity increases with solar proximity, releasing gases that form a visible coma.
Global monitoring
Ground-based telescopes in Hawaii and Spain track daily variations. The James Webb captures infrared images to map material distribution.
Data collected feed models on chemical evolution in protoplanetary disks. Collaboration involves more than 50 institutions in 20 countries.
Future trajectory
After perihelion, the comet will accelerate out of the Solar System. Final speed will exceed 40 km/swhen leaving the solar gravitational influence.
Passage through Mars’ orbit occurs in December 2025. Optical observations end in mid-2026 due to increasing distance.
Comparison with predecessors
Unlike 1I/Oumuamua, which did not show cometary activity, 3I/Atlas displays a gaseous tail. In relation to 2I/Borisov, it has a higher relative CO₂ content.
These variations indicate diversity in interstellar formation processes. Each object provides unique data about conditions in distant systems.
Technical Notes
High-resolution instruments detect specific emissions from molecules. Spectra confirm absence of fine dust common in local comets.
Sublimation rate increases 20% with every million kilometers closer to the Sun. Models predict peak brightness at magnitude 10 in the coming weeks.
