Comet 3I/ATLAS, the third interstellar object detected in the Solar System, will reach its closest proximity to Earth on December 19, 2025.
The North American space agency confirms that the celestial body will pass 270 million kilometers from the planet, a distance equivalent to almost twice the space between the Earth and the Sun.
This passage occurs after perihelion, the closest point to the Sun, recorded on October 29, and does not present any threat to humanity.
Astronomers from different countries are following the event to collect data on its composition and origin outside our stellar system.
Initial discovery and identification
The object was first spotted on July 1, 2025 by the ATLAS telescope in Chile, under the temporary designation A11pl3Z.
The following day, analyzes confirmed its interstellar nature, leading to the naming C/2025 N1 (ATLAS) and 3I/ATLAS, where “I” indicates interstellar origin and “3” marks the third known case.
- Initial observations revealed a coma of gas and dust stretching up to 350,000 kilometers.
- The recorded speed exceeds 210 thousand kilometers per hour, typical of visitors from other systems.
- Hubble images on July 21 showed the nucleus 445 million kilometers from Earth.
Trajectory through the Solar System
The hyperbolic orbit of 3I/ATLAS confirms that it does not return to our system, unlike native comets.
On October 3, it passed within 30 million kilometers of Mars, allowing observations by probes such as ExoMars and Mars Express.
After perihelion 210 million kilometers from the Sun, the comet accelerated to around 244 thousand kilometers per hour.
In November, it crossed close to Venus, 97 million kilometers away, and heads to Jupiter in March 2026.
Chemical composition revealed
NASA’s SPHEREx mission detected carbon dioxide in the comet’s coma, with a concentration eight times greater than that of water.
The James Webb Telescope has identified carbon monoxide and hydroxyl vapors, suggesting formation in a distant cold environment.
Studies indicate an age greater than seven billion years, older than that of the Solar System, which is 4.6 bmillions of years.
The presence of organohalogen compounds challenges traditional models of cometary formation.
Space agency observations
NASA has activated planetary defense protocols to track the object, but emphasizes the absence of risk.
Missions like Juno and Europa Clipper, focused on Jupiter, capture additional data about the visitor.
The European Space Agency uses the JUICE probe for remote analysis, with image transmission scheduled for February 2026.
Ground-based telescopes, such as the one at Teide in Spain, recorded 10,000-kilometer dust jets in August.
Recent behavior changes
After perihelion, the comet exhibited a color change and acceleration not explained by solar gravity alone.
It developed an anti-tail facing the Sun, visible in images from observatories in Austria.
These variations occur as the object moves away, making it the target of global astrometry campaigns.
Preliminary data indicate a core with a diameter between 440 meters and 5.6 kilometers.
Opportunity for science
3I/ATLAS offers insights into interstellar chemistry and planet formation processes in other stars.
Comparisons with 1I/’Oumuamua and 2I/Borisov highlight differences, such as the initial absence of a visible tail.
Astronomers predict that observations through December will reveal more about its internal structure.
The event reinforces the importance of detection networks like ATLAS for future visitors.