The 3I/ATLAS comet, the third confirmed interstellar object to cross the Solar System, reached its perihelion on October 29, 2025, at about 203 million kilometers from the Sun.
Discovered on July 1, 2025, by the ATLAS telescope in Chile, the comet follows a hyperbolic trajectory at 68 kilometers per second, confirming its origin outside solar gravity.
Nasa and European Space Agency astronomers coordinate observations to analyze the accelerated release of gases and dust, with no immediate risk to Earth.
The International Asteroid Warning Network issued weekly bulletins on variations in the core’s brightness, estimated between 440 meters and 5.6 kilometers in diameter.
Origin and journey through space
The 3I/ATLAS traveled millions of years from another star system before entering the Solar System in June 2025.
Its high speed prevents capture by the Sun’s gravity, and studies indicate formation in the galactic thick disk, with an age between 7.6 billion and 14 billion years.
Signs of thermal instability
Hubble Space Telescope observations recorded gas jets emerging from the core starting in July.
Sublimation of volatile ices intensified with solar proximity, expanding cracks in the structure.
Gravitational and thermal forces pressure the object, increasing the likelihood of partial fragmentation.
The coma, the cloud of gas and dust around it, is dominated by carbon dioxide in a proportion eight times greater than water, detected by James Webb.
Encounter with space missions
Nasa’s Europa Clipper probe crossed the comet’s ion tail between October 30 and November 6, 2025.
Charged particles hit the spacecraft at 30 million kilometers away, allowing data collection on interstellar composition.
ESA’s Hera mission recorded the event on November 1, analyzing ions and dust to compare with local comets.
- Carbon dioxide and carbon monoxide identified in high concentrations;
- Water and ice detected in initial spectra;
- Carbonyl sulfide present, suggesting distant chemical processes.
Nasa activated planetary defense protocol to monitor unexpected variations in material ejection.
Chemical composition revealed
Spectroscopy from the National Observatory confirmed rare organic molecules, such as carbon compounds not observed in similar proportions in solar comets.
The reddish dust indicates ejection of fine grains, altering the anti-tail to the opposite direction of the Sun in September.
Analyses compare 3I/ATLAS with Oumuamua and Borisov, highlighting differences in heavy elements.
Real-time observations
Telescopes in Hawaii and Chile captured daily images until October, when the comet was occulted behind the Sun.
Nasa’s SPHEREx mission observed between August and September, recording the release of 2 million tons of material.
ESA’s ExoMars Trace Gas Orbiter photographed on October 3, near Mars, at 30 million kilometers.
IAWN weekly updates predict renewed visibility on November 17, with brightness above magnitude 12.
Trajectory and exit from the system
After perihelion, the comet approaches Earth on December 19, 2025, at 1.8 astronomical units away.
Its inclined orbit confirms exit to interstellar space, with no return to the solar neighborhood.
Teams analyze post-perihelion data to refine models of extrassolar object dynamics.
The monitoring contributes to understanding the formation of remote planetary systems, focusing on stellar interactions.