Comet 3I/ATLAS, the third interstellar object ever identified to cross the Solar System, surprised the global scientific community by manifesting a series of unusual phenomena after its closest approach to the Sun. The anomalies include color changes, significant loss of mass and an acceleration that cannot be explained by the solar gravitational force alone. Observed by large telescopes such as James Webb and ALMA, the billion-year-old extrasolar visitor is providing unprecedented data on the formation of other planetary systems.
Discovered in July by telescopes from the ATLAS system, the celestial body follows a hyperbolic trajectory, indicating that it is not tied to solar attraction and will continue its course back to interstellar space. 3I/ATLAS joins the famous 1I/’Oumuamua and 2I/Borisov as objects that carry traces of chemistry and composition from regions outside the solar neighborhood. Its speed reaches approximately 221 thousand km/h.
Brightness change and core chromatic variations
The variation in the appearance of the 3I/ATLAS became one of the most notable points of its passage. Initially, the comet had a reddish hue, which gradually evolved into greenish and bluish tones as it approached and passed the Sun, reaching perihelion in October.
This chromatic transition is directly linked to the volatile composition of the comet and the way in which different gases are released and react to intense solar radiation.
- The initial red hue is attributed to the dust on its surface.
- The green color, observed later, suggests the presence of dicarbon (C₂) and cyanide (CN).
- The more recent shift to blue indicates the ejection of compounds such as cyanogen and ammonia in higher concentrations, or a strong emission of carbon monoxide gas (CO).
Data from solar probes such as STEREO-A, SOHO and GOES-19, monitoring the region close to the Sun, indicate that the comet’s brightness increased about five times between September and October. The brightness was expected to decrease rapidly after perihelion, but observations showed oscillations, suggesting an active and complex behavior of ice sublimation in its core.
Non-gravitational acceleration: the loss of mass
One of the most intriguing behaviors of 3I/ATLAS was its atypical acceleration, which slightly deviated it from the orbit predicted by gravitational calculations. During perihelion, exposure to solar heat caused massive sublimation of ice.
This degassing process is mainly responsible for the loss of mass of the celestial body, estimated at more than 13% of the core. The release of gases at high speed acts as a type of jet propulsion.
According to Harvard astrophysicist Avi Loebd, the values recorded for the radial and transverse acceleration are compatible with the impulse caused by this gas ejection. The ALMA Observatory, in turn, confirmed a deviation of four seconds of arc in relation to the calculated route. This acceleration, therefore, is not caused exclusively by gravity, but by the intrinsic activity of the comet.
Chemical composition: traces of an ancient system
The most recent studies on 3I/ATLAS indicate that it is one of the most massive interstellar objects ever detected, with a core that can range from 400 meters to 5.6 kilometers in diameter. Analysis carried out by the James Webb Space Telescope revealed a peculiar chemical composition, with high concentrations of carbon dioxide ($CO_2$), carbon monoxide ($CO$) and water ($H_2O$).
The comet’s coma, the cloud of gas and dust surrounding the nucleus, is dominated by carbon dioxide, which differs from the pattern of comets formed in our Solar System. This suggests that 3I/ATLAS formed in a stellar environment with different temperatures and planetary formation processes, potentially being older than the Sun itself. Scientists believe the comet may have wandered for billions of years, exposed to cosmic radiation, which shaped its current properties.
Global monitoring and the final route of the cosmic traveler
Currently, the interstellar comet is on its way out of the Solar System, but remains under intense monitoring by observatories around the world. The International Asteroid Warning Network (IAWN) plans international observation training between November and January to improveobject measurements. 3I/ATLAS will pass close to Earth in December, visible only with telescopes in the Northern Hemisphere. Each new data collected is a key piece in unlocking the mysteries of the diversity of celestial bodies and the evolution of stellar systems beyond our own. 3I/ATLAS is consolidated as a rare study opportunity.