Astronomers confirmed that comet 3I/ATLAS, discovered in July 2025 by the ATLAS telescope in Chile, follows a hyperbolic trajectory with a speed of 57 km/s, indicating its origin in another star system. The object, the third interstellar identified after ‘Oumuamua and Borisov, will not be captured by solar gravity and will leave the Solar System after passing close to the Sun on October 29. Observations from telescopes such as Hubble and JWST reveal active coma and dust, posing no risk to Earth.
Excessive speed allows 3I/ATLAS to avoid elliptical orbits, with orbital eccentricity greater than 6, greater than its predecessors. Calculations predict maximum approach to Earth in December 2025, at 1.8 astronomical units.
Initial discovery details
The ATLAS telescope detected the comet on July 1, 2025, 4.5 astronomical units from the Sun. Preliminary observations showed rapid movement and no local gravitational bond.
Confirmed as interstellar on July 2 by the Minor Planet Center, the 3I designation reflects its position in the sequence of external visitors. Telescopes in Chile, Arizona and Hawaii have identified a marginal coma and a 3-arc-second tail.
Pre-discovery data from June 2025 extended the trace and validated hyperbolicity.
3I/ATLAS Is Not Behind the Sun.
— 3I/ATLAS (@3IAtlas_Anomaly) October 28, 2025
Astronomers were told the interstellar object would disappear behind the Sun during its Oct 29 perihelion. But new observations show that’s not true.
On Oct 25, the team recorded 3I/ATLAS visible beside the Sun — not hiddenden.
Position: RA 13h 38m… pic.twitter.com/cqRoIn8PGT
Trajectory and record speed
The speed of 57 km/s represents the record for interstellar objects, surpassing ‘Oumuamua at 26 km/s and Borisov at 32 km/s. This rate, measured as infinite speed, confirms ejection from another stellar system billions of years ago.
The hyperbolic orbit, with an inclination of 175 degrees in retrograde motion, indicates previous galactic interaction. The perihelion occurred at 1.36 astronomical units, between the orbits of Earth and Mars.
- Eccentricity: about 6.14, the highest recorded;
- Minimum distance to Earth: 1.8 AU in December 2025;
- Exit direction: towards the constellation Virgo, towards interstellar space.
Computer models simulate the effect of “assisted gravity”, where the Sun changes course without capturing the object.
Chemical composition revealed
Spectroscopic analyzes detected common elements, but in different proportions from solar comets, such as a greater presence of gaseous nickel at cold distances. The James Webb Space Telescope in August 2025 identified primitive isotopes and irradiated crustby ancient cosmic radiation.
The reddish coma suggests silicate-rich dust, similar to Borisov, but with high organohalogen fractions. Observations from the Nordic Optical Telescope confirmed diffuse-looking activity in July.
Results indicate an age between 7.6 and 14 billion years, linked to ancient stellar populations in the Milky Way.
Observed non-gravitational acceleration
During perihelion, 3I/ATLAS exhibited an acceleration of 0.02 mm/s², attributed to the ejection of gases due to solar heating, similar to ‘Oumuamua in 2017. This force does not change the hyperbolicity, but causes an estimated mass loss of 50% over months.
Data from the Swift Observatory detected hydroxyl and water ice, explaining the “push” without evidence of artificial propulsion. The bluish color, observed in October, results from a gaseous cloud formed by sublimation.
ESA’s Juice probe plans observations in November 2025 to map emissions.
Comparison with previous visitors
‘Oumuamua, discovered in 2017, measured 400 meters and accelerated by hydrogen degassing, with no visible coma. Borisov, in 2019, showed an active tail and organic composition, but lower speed.
3I/ATLAS differs by estimated size of 1 to 10 km and rapid brightness, inverting spectral tilt to blue.
- ‘Oumuamua: elongated shape, anomalous acceleration;
- Borisov: red coma, high carbon fractions;
- 3I/ATLAS: icy core, distant vaporized nickel.
These differences highlight variety in exoplanetary systems.
Real-time observations
Ground-based telescopes have been tracking the comet since November 2025, with magnitude 14.7 visible on 20-cm aperture instruments before dawn in Virgo. The Mars Express probe captured images in October at 19 million km.
GOES-19 recorded solar conjunction on October 21, confirming orbital stability. Global campaigns with VLT and Keck extend data until March 2026.
Post-perihelion brightness stabilized, with four-component tail without breaks.
