Astronomers confirmed the detection of comet 3I/ATLAS, the third known interstellar object, by the ATLAS system in the Atacama Desert, in Chile, on July 1, 2025. The celestial body, originating from another stellar system, moves in a hyperbolic trajectory at more than 61 km/s, with no gravitational connection to the Sun. This passage allows detailed analyzes of materials formed in distant environments, without posing a threat to Earth, with minimum distance of 270 million kilometers.
The comet reached perihelion on October 29, 2025, 210 million kilometers from the Sun, and recent observations show increasing gaseous activity. Telescopes like the James Webb have captured infrared data that reveal their unique composition. International teams coordinate monitoring to map changes on the surface.
- Preliminary observations indicate a core of about 1 km in diameter.
- The speed of sublimation of gases increases 20% for every million kilometers of approach to the Sun.
- No fragmentation has been recorded so far, despite the solar proximity.
Initial detection by the ATLAS system
The ATLAS telescope, funded by NASA and located in Río Hurtado, identified the object during routine scans in June 2025. Preliminary archival data revealed images from June 14, confirming the interstellar origin by orbital eccentricity greater than 6. Calculations by the International Astronomical Union validated the classification within days.
Teams at the European Southern Observatory and Hawaii contributed independent confirmations. The low orbital inclination, close to the ecliptic plane, facilitated initial tracking. May observations by NASA’s TESS satellite suggest early cometary activity, 6.4 astronomical units from the Sun.
Chemical analysis of coma and tail
Spectra obtained by the Hubble Space Telescope on July 21, 2025 showed a reddish coma, indicative of fine dust. The presence of water vapor and carbon monoxide differentiates 3I/ATLAS from typical solar comets. Analysis by the Very Large Telescope in Chile has detected nickel vapor at high levels, measured by spectrographs over multiple days.
Frozen carbon dioxide dominates the surface, suggesting formation at temperatures below -100°C. The release of gases forms a 0.5 arc minute tail, pointing east, away from the Sun by radiation pressure. Chemical evolution models compare this data with protoplanetary disks from other systems.
Studies indicate that the object may be more than 7 billion years old, originating in the thick disk of the Milky Way. The reddish color of the coma evolved to more intense tones in July, reflecting changes in the composition. Cyanide and carbonyl sulfide levels were quantified in October observations.
Global monitoring and collaborations
Ground-based telescopes in Gavaí, Spain and Australia record daily variations in luminosity. The Gemini South Observatory in Chile captured images on August 27, 2025, revealing a condensed coma with a bright core. More than 50 institutions from 20 countries are part of the effort, coordinated by the Minor Planet Center.
The European Space Agency used the Mars Express and ExoMars Trace Gas Orbiter probes for observations in October, 19 million kilometers away. Data from the GOES-19 satellite captured the comet during solar conjunction on October 21. The Vera C. Rubin Telescope, operating in Chile, has expanded early detection.
- The International Asteroid Warning Network conducts precise astrometry exercises.
- James Webb’s NIRSpec instrument mapped material distributions on August 6.
- Radio observations look for emissions from molecules such as hydroxyl.
Future trajectory and exit from the Solar System
After perihelion, 3I/ATLAS accelerates beyond 40 km/s, crossing the orbit of Mars in December 2025. The solar gravitational influence gradually decreases, allowing interstellar exit. Optical observations end in mid-2026 when the distance exceeds detection limits.
The non-gravitational acceleration, measured at 1.662 × 10⁻⁶ au/day², suggests additional forces such as gas ejection. Models predict peakbrightness at magnitude 10 in the coming weeks, visible in amateur telescopes. The passage through Gemini in 2026 marks the definitive goodbye.
The object follows an orbital plane aligned with the planets, passing close to Jupiter and Venus. Probes such as Europa Clipper and Hera may cross its tail between October 30 and November 6, 2025. Minimum distance to Earth occurs on December 19, at 271 million kilometers.
Comparisons with previous visitors
Different from 1I/ʻOumuamua, discovered in 2017 without cometary activity, 3I/ATLAS displays a prominent gaseous tail. In relation to 2I/Borisov from 2019, it presents a higher relative concentration of CO2, with less water vapor. These differences highlight variations in interstellar formation processes, providing insights into conditions in remote systems.
Spectral analyzes confirm the absence of fine dust typical of local comets, with specific molecular emissions. The detection of hydroxyl by the Neil Gehrels Swift Observatory reinforces the presence of water, a marker of potential habitability at distant origins. Each object adds unique layers to the catalog of cosmic interlopers, refining galactic models.
Recent observations and anomalies detected
On October 25, 2025, teams recorded the comet visible close to the Sun, contradicting occultation predictions. Images from the CCOR-1 coronagraph on the GOES-19 satellite show a position in right ascension at 13h 38m, without solar shadowing. The luminosity stabilized at magnitude 14.7, with a coma of 0.6 arc minutes.
Special changesctrals for bluish tones occurred near perihelion, with an excess temperature of 5,000 K. The continuous acceleration in the orbital plane, without a vertical component, intrigues modelers. Observations by the Instituto de Astrofisica de Canarias confirmed activity on July 2, with a tail lengthening of 3 arc seconds.
The composition evolves with sublimation, releasing organohalogens fractionated at +650‰. Data from the Canada-France-Hawaii Telescope reveals elongated ellipsoid at core. Astrometric campaign from November 2025 to January 2026 refines orbit, integrating amateur contributions.
Technical measurement details
High-resolution instruments identify emissions from molecules such as cyanide and nickel at 1,000 K. Spectra from the Nordic Optical Telescope on July 2, 2025 exhibit active diffuse appearance. The sublimation rate projects maximum brightness at magnitude 10, accessible to 15-25 cm telescopes.
Observations from the Transiting Exoplanet Survey Satellite indicate activity since May 2025. The reddish coma, similar to 2I/Borisov, darkened in July due to dust. Models predict no flares so far, with constant brightness levels.