NASA: Interstellar comet 3I/Atlas reaches perihelion on October 29 and departs Earth’s sky

The GOES-19 satellite recorded comet 3I/ATLAS on October 18, 2025, using the CCOR-1 coronagraph. The object appears as a discrete point, obscured by solar glare. The National Oceanic and Atmospheric Administration (NOAA) operates the equipment in geostationary orbit.

Citizen scientist Worachate Boonplod identified the comet in the image. 3I/ATLAS reaches perihelion on October 29, at 1.36 astronomical units (AU) from the Sun. The distance equals about 203 million kilometers.

• Discovery occurred on July 1, 2025.
• Hyperbolic trajectory confirms interstellar origin.
• Maximum Earth approach scheduled for December 19.

Discovery and orbital characteristics

Astronomers detected 3I/ATLAS on July 1, 2025. The object was positioned on the opposite side of the Sun from Earth. Ground-based telescopes captured the initial data.

The hyperbolic orbit indicates speed exceeding solar escape velocity. The comet remains unbound to the solar system. It originates from another stellar system.

Orbital inclination reaches high values. The plane differs significantly from the planetary ecliptic.

Passage near Mars

The comet crossed Mars’ orbit on October 3, 2025. Minimum distance to the red planet remained safe. Observations confirmed the predicted path.

Instruments recorded initial brightness variations. Proximity to the Sun increases cometary activity. Gases sublimate from the frozen nucleus.

Coronagraph operation

The CCOR-1 coronagraph blocks the central solar disk. An artificial occulter simulates a total eclipse. The technique enables study of the outer solar corona.

In the October 18 image, the comet appears at the field periphery. The luminous point maintains consistent position across sequential frames. Analyses confirm identity with 3I/ATLAS.

GOES-19 maintains fixed position relative to Earth. Geostationary orbit facilitates continuous monitoring.

Current alignment with the Sun

On October 26, 2025, the comet aligns directly behind the Sun. Minimum angular elongation prevents ground-based observations. Telescopes face solar glare interference.

Jet Propulsion Laboratory (JPL) simulations display the configuration. Earth, Sun, and comet form an approximate straight line. Angular separation reduces to fractions of a degree.

Perihelion and expected activity

Perihelion occurs on October 29 at 1.36 AU. The distance places the comet inside average Martian orbit. Solar radiation intensifies volatile sublimation.

Models predict increase in dust and gas production. The coma expands significantly. The tail may extend millions of kilometers.

Composition includes typical interstellar comet elements. Spectroscopy reveals carbon monoxide and cyanide presence.

Emergence from solar glare

Terrestrial visibility improves from November 8. The comet moves angularly away from the Sun. Elongation grows daily.

On November 11, it appears in the eastern morning sky. Observers locate the object 90 minutes before sunrise. Virgo constellation serves as reference.

Spica star marks initial nearby position. The comet moves against the stellar background.

Requirements for amateur observation

Telescopes with minimum 20 cm aperture are necessary. Predicted magnitudes range between 13 and 14. Dark sky conditions favor detection.

Narrowband filters aid coma identification. CCD cameras record long exposures. Processing software removes noise.

Brazilian astronomers obtained pre-conjunction images. Cristóvão Jacques used remote equipment. Diego contributed photometric data.

Detailed light curve

Apparent magnitude peaks near 13 at perihelion. Values decrease post-passage. Increasing distance reduces brightness.

Initial observations recorded magnitude 18 at discovery. Recent data indicate value near 14. European Space Agency (ESA) projections validate the model.

Geometric factors influence visibility. Comet phase varies continuously.

Juice mission conducts two observations

Juice probe observes the comet on November 2. Optical instruments and spectrometers collect data. Post-perihelion proximity maximizes activity.

Second session occurs on November 25. Spacecraft positioning remains favorable. High-resolution images capture tail structure.

Data contribute to comparative studies. 3I/ATLAS differs from native solar comets.

Ideal configuration in January

On January 25, 2026, Earth and comet align opposite the Sun. Frontal illumination highlights coma details. Tail points away from the star.

Maximum angular separation facilitates tracking. Professional telescopes obtain detailed spectra.

Proximity to Jupiter

Comet crosses Jovian orbital plane on March 20, 2026. Minimum separation to gas giant enables joint observations. Jupiter serves as bright reference.

Configuration favors precise astrometry. Measurements refine orbital parameters.

Confirmed interstellar origin

Dynamic analyses exclude solar system origin. Orbital eccentricity exceeds 1. Hyperbolic velocity reaches 30 km/s at entry.

Comparisons with 1I/’Oumuamua and 2I/Borisov show similarities. Three known objects share kinematic characteristics.

Expected chemical composition

Spectra indicate complex organic compounds. Molecules like hydrogen cyanide appear in emissions. CN and C2 radicals contribute to coloration.

Carbon-nitrogen ratio differs from local comets. High values suggest formation in cold interstellar environment.

Scientific contributions

3I/ATLAS provides third interstellar sample. Data complement previous studies. Planet formation models gain constraints.

Multi-wavelength observations cover radio to ultraviolet. Global networks coordinate campaigns.

Observation protocols

Astronomers follow standard procedures for transient objects. Alerts circulate via Central Bureau for Astronomical Telegrams. High priority assigned due to scientific interest.

Southern hemisphere stations contribute significantly. Sites in Chile and South Africa offer favorable windows.

Computational simulations

Numerical models reproduce trajectory with precision. Integrations consider planetary perturbations. Non-gravitational effects include asymmetric jets.

Brightness predictions incorporate sublimation rate. Nucleus parameters estimated at tens of meters.

Impact on astronomical community

Object generates interest beyond specialists. Science outreach programs highlight rarity. Three interstellar visitors in eight years mark new era.

Schools incorporate topic in curricula. Practical activities involve visual search.

Future after passage

Comet accelerates outward from solar system post-perihelion. Asymptotic velocity maintains original direction. Final trajectory points to specific constellation.

Monitoring continues for decades with space telescopes. Infrared sensors detect residual thermal signature.

Observational legacy

Archived data remain available for future generations. Databases like Planetary Data System host complete sets. Later analyses reveal subtle patterns.

3I/ATLAS consolidates interest in external visitors. Future missions plan direct interception.