What is 3I/ATLAS? comet from outside the Solar System crosses inner orbit on hyperbolic trajectory
The comet 3I/ATLAS was discovered on July 1, 2025 by the ATLAS telescope system, funded by NASA, in Chile. Astronomers confirmed its origin outside the Solar System through the hyperbolic orbit, which indicates a single-pass trajectory without gravitational capture by the Sun. The object received the designation “3I” for being the third interstellar detected, after 1I/’Oumuamua in 2017 and 2I/Borisov in 2019.
Initial observations showed cometary activity, with a coma and tail formed by sublimation of ice. The speed relative to the Sun reaches about 60 km/s.
- Discovery: July 1, 2025
- Telescope: ATLAS in Chile
- Type: interstellar active comet
- Perihelion: end of October 2025
Origin and trajectory
3I/ATLAS has been traveling through interstellar space for billions of years, likely expelled from a distant star system in the Milky Way. Its hyperbolic orbit has an eccentricity greater than 6, a value that confirms its external origin.
The object entered the inner Solar System on an inclined trajectory and reached perihelion on October 30, 2025, at approximately 1.4astronomical unit of the Sun, within the orbit of Mars. The minimum distance from Earth is around 1.8 AU, without any risk of collision.
Physical characteristics
The comet’s nucleus measures between 1 and 5.6 kilometers in diameter, according to estimates from the Hubble Space Telescope. The composition includes water ice, carbon dioxide and other volatiles that sublime when approaching the Sun.
Observations reveal diffuse coma and tails of dust and ions, with intense release of water vapor and hydroxyl detected by ultraviolet telescopes.
The activity began early, still 6.4 AU from the Sun, driven by ices more volatile than water.
Activity observed
The comet developed a visible coma days after its discovery, confirmed by telescopes in Hawaii, Arizona and Chile. Hubble images in July 2025 recorded a dust plume and faint tail.
Observatories such as Gemini South and JWST identified an antisolar tail and constant growth of the coma. The release of gases forms tails that extend for tens of thousands of kilometers.
Scientific importance
3I/ATLAS offers a rare opportunity to study primordial material from another star system. Spectroscopic analyzes compare their chemistry to solar comets, revealing similarities and differences in planetary formation.
Agencies such as NASA and ESA coordinate observations with ground-based telescopess, Hubble, JWST and probes on Mars and Jupiter. The data refines models about interstellar objects and their frequency in the galaxy.
Observations in progress
Global telescopes follow the comet after perihelion, with renewed visibility in December 2025. Missions such as Mars Express and Juice record the object from distant points in the Solar System.
The absence of fragmentation or outbursts keeps the activity stable. The comet will leave the Solar System in 2026, heading to the constellation Gemini.
