NASA monitors 3I/ATLAS: speed rises to 244,000 km/h and trajectory changes near the Sun in October
The North American Space Agency confirmed that comet 3I/ATLAS, identified as the third interstellar object to cross the Solar System, accelerated significantly past its closest point to the Sun. The event occurred on October 29, 2025, 1.4 astronomical units away, equivalent to 210 million kilometers. This change in speed and trajectory occurs due to the solar gravitational influence, without the risk of collision with Earth.
Astronomers detected the comet on July 1, 2025, using the ATLAS telescope in Chile. Its hyperbolic orbit, with an eccentricity greater than 6, indicates an origin external to the Solar System and a permanent exit after perihelion. The current speed reaches around 244 thousand kilometers per hour, with an approach to Earth scheduled for December, at 1.8 AU or 270 million kilometers.
Preliminary observations reveal a composition rich in carbon dioxide, eight times greater than water in the coma, which arouses scientific interest. The James Webb Space Telescope captured data in August confirming carbon monoxide and hydroxyl vapors formed in distant cold environments.
Unusual chemical composition
Data from James Webb indicate that the 3I/ATLAS coma predominates in CO₂, with the presence of haloorganic compounds and the absence of iron linked to nickel. This configurationDoes not challenge traditional models of solar comets.
The reddish color observed by Hubble in July suggests silicate-rich dust, evolving to bluer tones near perihelion due to ionized emissions.
- High concentration of carbon dioxide in the coma;
- Carbon monoxide vapors detected in August 2025;
- Absence of prominent tail, unlike 2I/Borisov;
- Estimated age between 7 and 14 billion years, prior to the Solar System.
These elements point to the formation of another star in a cold and remote region.
Intensified global monitoring
Astronomers have been coordinating observations since November 2025 with telescopes in Chile, Hawaii and Australia. Hubble recorded images in July, showing a drop-shaped coma with ejected dust.
The European Space Agency contributed to Mars Express in October, collecting data from 19 million miles away. The Juice mission will attempt captures in November using cameras and spectrometers.
The comet became invisible during the solar conjunction, reappearing in December for professional telescopes.
Planetary trajectory and passages
3I/ATLAS follows a hyperbolic orbit, confirmed by measurements from the Minor Planet Center. Its speed increased to 244 thousand km/h post-perihelion,no non-gravitational acceleration detected until November.
In November, it will pass Venus at 97 million kilometers. In March 2026, it will approach Jupiter at 54 million kilometers, allowing studies of gravitational interactions.
- Minimum distance to the Sun: 1.4 AU on October 29;
- Approach to Earth: 1.8 AU in December 2025;
- Passage by Venus: November 2025, 97 million km;
- Encounter with Jupiter: March 2026, 54 million km.
These distances guarantee safety for inner planets.
Interstellar origin confirmed
The hyperbolic orbit excludes capture by solar gravity, with a trajectory suggesting ejection from another stellar system billions of years ago. Alignment close to the ecliptic plane, within 5 degrees, has a probability of 0.2%.
Studies indicate formation in the center of the Milky Way, with thick radiated crust simulated by models. SPHEREx observations in August reinforce primordial composition, offering clues about outer planetary formation.
The object, with a diameter estimated at 440 meters to 5.6 kilometers, exhibits stable activity without explosions, monitored since May 2025 by TESS.
Expected scientific contributions
Research until January 2026 aims to map chemistry interstellar, with Webb data revealing water ice and carbonyl sulfide. The lack of a clear post-perihelion tail, noted in images from November 5, questions models of dust ejection.
The campaign includes missions like Perseverance and Curiosity on Mars, as well as Lucy and Psyche. These records enhance understanding of transient objects.
The unique composition, without nickel iron, tests hypotheses of cometary evolution, contributing to studies of exoplanets.
