Astronomers from the Minor Planets Center have confirmed that comet 3I/ATLAS, detected in July 2025 by the ATLAS telescope in Chile, originates from outside the Solar System. The object travels at a speed of 57 km/s in a hyperbolic orbit, which prevents it from being captured by solar gravity. This trajectory was observed by instruments such as Hubble and James Webb, revealing an active coma and dust, posing no risk to Earth.
The detection occurred 4.5 astronomical units from the Sun, with rapid movement indicating the absence of local gravitational ties. Preliminary observations in July highlighted a marginal coma and three arcsecond tail.
Calculations indicate that perihelion occurred on October 29, 2025, at 1.36 astronomical units, between the orbits of Earth and Mars.
Initial detection details
The ATLAS telescope identified the comet on July 1, 2025, at an initial distance of 4.5 astronomical units. June data extended the orbit and confirmed hyperbolicity.
Instruments in Chile, Arizona and Hawaii recorded diffuse activity shortly after discovery. The 3I designation reflects its position as the third interstellar visitor.
3I/ATLAS не находится за Солнцем.
— 3I/ATLAS (@3IAtlas_Anomaly) 28 октября 2025 г.
Астрономам сообщили, что межзвездный объект исчезнет за Солнцем во время его перигелия 29 октября. Но новые наблюдения показывают, что не так. команда зафиксировала3I/ATLAS, видимую рядом с Солнцем, а не скрытую.ден.
Позиция: RA 13ч 38м… pic.twitter.com/cqRoIn8PGT
Trajectory and record speed
The speed of 57 km/s surpasses ‘Oumuamua’s 26 km/s and Borisov’s 32 km/s, measuring itself as infinite speed. This rate suggests ejection from another stellar system billions of years ago.
The hyperbolic orbit has an eccentricity of 6.14 and an inclination of 175 degrees, with retrograde movement. Computer models simulate the effect of the Sun’s gravitational assistance, altering its course without capture.
- Eccentricity: about 6.14, the highest recorded;
- Minimum distance to Earth: 1.8 astronomical units in December 2025;
- Exit direction: into interstellar space towards the constellation Virgo.
Chemical composition revealed by analysis
Spectroscopy detected elements common to solar comets, but with different proportions, such as a greater presence of nickel gas in cold regions. The James Webb Telescope identified primitive isotopes and crust irradiated by ancient cosmic rays in August 2025.
Eat itred indicates dust rich in silicates, similar to Borisov, but with high fractions of organic halogens. Observations from the Nordic Optical Telescope confirmed diffuse activity in July.
Results point to an age between 7.6 and 14 billion years, linked to ancient stellar populations in the Milky Way. This composition highlights differences between exoplanetary systems.
The comet exhibits non-gravitational acceleration of 0.02 mm/s² during perihelion, caused by the ejection of gases due to solar heating, similar to that observed in ‘Oumuamua in 2017. This force does not change the hyperbolicity, but estimates a 50% mass loss over months.
Data from the Swift observatory revealed hydroxyl and water ice, explaining the thrust without evidence of artificial motion. The bluish color observed in October results from a gaseous cloud formed by sublimation.
Observed non-gravitational acceleration
The phenomenon occurs due to the release of gases, without altering the interstellar origin. Estimates predict significant mass loss in the coming months.
Comparisons with previous visitors
‘Oumuamua, detected in 2017, measured 400 meters and accelerated due to hydrogen degassing, with no visible coma. Borisov, from 2019, exhibited an active plume and organic composition, but slower velocity.
3I/ATLAS differs in size from an estimated 1 to 10 km and high brightness, with a blue-inverted spectral tilt. These variations emphasize diversity of exoplanetary origins.
- ‘Oumuamua: elongated shape, anomalous acceleration;
- Borisov: red coma, high carbon fractions;
- 3I/ATLAS: icy core, distant evaporated nickel.
Real-time observations
Ground-based telescopes have been monitoring the comet since November 2025, with a stellar magnitude of 14.7 visible on 20-cm aperture instruments before dawn in Virgo. The Mars Express probe captured images 19 million kilometers away in October.
The GOES-19 satellite recorded solar conjunction on October 21, confirming orbital stability. Global campaigns with VLT and Keck extend data until March 2026.
The post-perihelion brightness stabilized, with a four-component tail without breaks. The European Space Agency plans observations with the Comet probe in November to map ejections.
