Traveling at a speed exceeding 30 km/s along a hyperbolic trajectory, comet 3I/Atlas crosses the Solar System as the third confirmed interstellar object in history. The Atlas system in Chile identified the body on July 1, 2025, opening a direct window for researchers to examine materials formed in distant stellar environments outside our own neighborhood.
Research teams operate instruments such as the James Webb Space Telescope to examine the chemical makeup of the visitor. The object presents zero collision risk to Earth, maintaining a minimum safe distance of 270 million kilometers from the planet. Tracking campaigns follow the path toward perihelion, the point of closest approach to the Sun, at a distance of 210 million kilometers.
Spectroscopic readings point to a high concentration of carbon dioxide ice across the structure. The simultaneous presence of carbon monoxide and water vapor sets the visitor apart from comets native to the Solar System, while orbital calculations show that gravitational forces ejected the body 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
Routine observations in the Atacama Desert confirm unbound orbit
Engineers and astronomers operating the Atlas system in the Atacama Desert logged the initial images during standard sky surveys in Chile. Early positional measurements immediately indicated an open orbit that was not gravitationally bound to the Sun.
Follow-up mathematical models verified that the object moves at an escape velocity higher than the threshold of the Solar System. Within a few days of the July 1, 2025 sighting, international astronomy teams reviewed the trajectory and officially validated its classification as an interstellar comet.
Surface formed below -100°C holds predominantly frozen carbon dioxide
Detailed spectroscopic analyses show that frozen carbon dioxide dominates the outer layer of 3I/Atlas. According to the research data, this specific concentration indicates that the object coalesced at temperatures below -100°C within the cold, outer regions of a foreign star system.
Water vapor appears in smaller proportions than those typically measured in local solar comets, while carbon monoxide rounds out the volatile profile detected by sensors. Brightness estimates indicate a solid core measuring approximately 1 kilometer in diameter, and the increasing proximity to solar radiation triggers cometary activity that releases gases into a visible coma.
More than 50 institutions in 20 countries map infrared emissions
Ground-based observatories located in Spain and Hawaii monitor daily fluctuations in the structure of the comet. Working in tandem from space, the James Webb captures infrared images that allow scientists to map how material is distributed across the coma and core.
Read also: James Webb Space Telescope detects methane gas on interstellar comet 3I/ATLAS for the first time
The global monitoring effort brings together more than 50 institutions across 20 countries. All observational data collected during the passage feed directly into computer models designed to simulate chemical evolution inside protoplanetary disks.
Gravity will accelerate the object above 40 km/s past Mars
Once 3I/Atlas completes its passage around perihelion, solar gravity will sling the body outward and accelerate its departure from the Solar System. The final velocity will surpass 40 km/s as the comet exits the zone of solar gravitational influence for good.
The outbound route crossed the orbit of Mars in December 2025. Because the distance between the object and Earth grows rapidly after that point, optical observations from ground and space telescopes conclude in mid-2026.
Gaseous tail and absence of fine dust distinguish 3I/Atlas from 1I/Oumuamua and 2I/Borisov
Direct comparisons with the two previous interstellar visitors highlight physical differences among objects arriving from deep space. Unlike 1I/Oumuamua, which passed through the Solar System without displaying any cometary activity, 3I/Atlas maintains an active gaseous tail, and it carries a higher relative concentration of carbon dioxide than the second confirmed visitor, 2I/Borisov.
Astronomers note that these chemical and structural variations point to diverse planetary formation processes across the galaxy, with each captured object supplying unique parameters about distant stellar environments. High-resolution instruments tracking molecular emissions from 3I/Atlas also confirmed the absence of the fine dust particles commonly found in local comets:
- Core diameter estimated by brightness: about 1 kilometer
- Minimum distance from Earth: 270 million kilometers
- Perihelion distance from the Sun: 210 million kilometers
- Sublimation rate increase: 20% for every million kilometers closer to the Sun
- Predicted peak brightness: magnitude 10
As the comet approaches the inner Solar System, the rate at which its surface ice turns directly into gas rises by 20% with every million kilometers of solar proximity. Observational models set the peak brightness of 3I/Atlas at magnitude 10 during its closest approach.
