The comet 3I/ATLAS, the third detected interstellar object, will reach perihelion on October 29, 2025, at 1.36 astronomical units from the Sun. Discovered in July 2025 by the ATLAS telescope in Chile, the body follows a hyperbolic orbit with eccentricity greater than 5. The close approach exposes the nucleus to intense radiation, potentially causing volatile evaporation and fragmentation.
Recent observations show dust and ice jets pointing toward the Sun. Images from the Nordic Optical Telescope between July and September 2025 recorded extreme negative polarization. The composition rich in carbon dioxide and metals suggests formation in a cold environment of another star system.
- Speed reaches 245,000 km/h.
- Minimum distance equals 203 million kilometers.
- Trajectory places the comet between the orbits of Earth and Mars.
Anomalies recorded in the nucleus
Astronomers identified a sudden brightness increase in 3I/ATLAS. The phenomenon indicates ejection of internal material.
The extreme negative polarization sets the comet apart from known objects. Data point to formation in a region similar to an external Kuiper Belt.
Trajectory and solar proximity
The 3I/ATLAS currently transits behind the Sun from Earth’s perspective. Coronagraph telescopes like CCOR-1 on the GOES-19 satellite maintain monitoring.
A Thai amateur astronomer captured images on October 21, 2025. The photos reveal a gas and dust coma despite intense solar glare.
After perihelion, the comet will emerge visible at dawn. Constellations such as Virgo and Leo will host the object in November.
Contributions from space missions
NASA’s Europa Clipper probe will cross the comet’s ion tail in late October. The distance will be 300 million kilometers from the Sun.
ESA’s Juice mission will pass 64 million kilometers away on November 4. Instruments will conduct multi-spectral composition measurements.
These encounters will provide data on charged particles. The analyses will verify post-perihelion nucleus integrity.
Post-perihelion monitoring
Ground-based telescopes will resume observations in November and December 2025. The comet will gradually move away from the Sun.
On November 3, the object will pass 0.65 astronomical units from Venus. Sky survey networks will detect possible dust trails.
Lessons from previous comets
The 2I/Borisov fragmented in March 2020 after perihelion in December 2019. The Hubble Telescope recorded the nucleus splitting into two pieces separated by 180 kilometers.
The breakup occurred at 2 astronomical units from the Sun. Analyses revealed water and organic compounds similar to local comets.
The process accelerated rotation to the breaking point. Dust release enabled detailed chemical studies.
Preparation for future events
Astronomers maintain watch over 3I/ATLAS in March 2026. The comet will cross Jupiter’s orbit at 54 million kilometers.
The Juno probe will record gravitational interactions. Monitoring strengthens telescope networks for hyperbolic objects.
Relative speed of 60 km/s characterizes interstellar visitors. Catalogs expand with each documented passage.
