Astronomers from the National Aeronautics and Space Administration (NASA) and the European Space Agency (ESA) are monitoring the trajectory and chemical makeup of 3I/ATLAS, the third object of extrasolar origin ever identified in our solar system. Detected on July 1, 2025, by the Asteroid Terrestrial-impact Last Alert System (ATLAS) telescope in Chile, the body travels along a hyperbolic path and emits an unusual bluish glow. The object reached its perihelion, the point of closest approach to the Sun, on October 30, 2025, at a distance of 1.4 astronomical units (AU), a unit of measurement equal to the average distance between the Earth and the Sun. The passage posed no threat to Earth, which remained at a safe distance of 1.8 AU.
Coordinated international campaigns are analyzing the object’s trajectory and outgassing to understand its ancient galactic origins. Computer models and astronomical observations indicate that the comet formed prior to our solar system, with age estimates ranging between 7 billion and 14 billion years. Active cometary behavior, including a diffuse coma and a dust tail, was documented in July 2025 when the Hubble Space Telescope captured images of the nucleus and material ejections.
Retroactively processed tracking data from June 2025 confirmed the hyperbolic orbit and a velocity of 137,000 km/h. Initial measurements established several baseline physical parameters for the interstellar visitor:
- Coma diameter: expanded from 13,000 km to 18,000 km during July 2025.
- Brightness stability: no sudden luminosity outbursts were recorded, indicating structural stability.
- Initial chemical traces: early spectroscopic readings confirmed the presence of carbonyl sulfide and water vapor.
Telescopes in three countries tracked the initial dust coma
The ATLAS facility in Chile first spotted 3I/ATLAS as a faint, fast-moving point of light, which prompted immediate calculations that verified its interstellar provenance. Ground-based observatories in Hawaii, Chile, and Australia activated rapid-response observation protocols to lock onto the target. On July 21, 2025, the Hubble Space Telescope recorded a reddish dust coma surrounding the central nucleus.
Close approaches to Mars and Venus enabled spacecraft readings
As the comet traveled through the inner solar system, its path brought it within 30 million kilometers of Mars on October 3, 2025. This proximity allowed orbital spacecraft, specifically the Mars Express and the ExoMars Trace Gas Orbiter, to collect spectral data directly from the passing body. Maintaining its hyperbolic speed of 137,000 km/h, the comet subsequently passed within 97 million kilometers of Venus on November 3, 2025, without experiencing significant gravitational interactions.
Space-based observatories also targeted the object across different wavelengths. The James Webb Space Telescope observed outgassing activity on August 6, 2025, while ESA scheduled advanced sensor recordings for November 2025 using its Jupiter Icy Moons Explorer (Juice) mission. After passing behind the Sun from Earth’s perspective, the comet’s reappearance on October 31, 2025, restored visibility for ground telescopes, following solar conjunction monitoring conducted by the Solar and Heliospheric Observatory (SOHO) and the Polarimeter to Unify the Corona and Heliosphere (PUNCH).
Spectroscopy reveals carbon dioxide dominance and color shifts
Data gathered by the James Webb Space Telescope and the Spectro-Photometer for the History of the Universe, Epoch of Reionization and Ices Explorer (SPHEREx) identified carbon dioxide as the dominant component in the comet’s coma, while water ice and carbon monoxide appeared in smaller quantities. Cyanide gas and nickel vapor were measured in proportions comparable to those found in native solar system comets, though the initial reddish coma was found to originate from micrometer-sized dust grains.
As 3I/ATLAS moved closer to the Sun, its color shifted toward a bluish hue, pointing to surface alterations caused by sublimation without any visible loss of mass. In July and August 2025, the Neil Gehrels Swift Observatory recorded water vapor emissions alongside an increase in nickel content driven by solar heating.
NASA confirms natural cometary physics after anomaly claims
The physical behavior of the object sparked academic debate after scientists noted non-gravitational acceleration without visible mass loss, paired with an irregular rotation. Harvard researcher Avi Loeb cataloged these characteristics as eight distinct anomalies.
Despite the unusual readings, NASA classifies 3I/ATLAS as a natural comet with no evidence of technological origin. The agency bases this conclusion on spectral analyses that remain fully consistent with standard gas sublimation processes.
Models trace the object to the thick disk of the Milky Way
Kinematic simulations suggest an age between 7.6 billion and 14 billion years for 3I/ATLAS, placing its birthplace in the thick disk of the Milky Way, an ancient region rich in stars but poor in heavy elements. Broader analytical ranges place the age between 3 billion and 11 billion years, supported by a high vertical velocity that indicates an inclined galactic orbit altered by gravitational encounters with stars over billions of years. Having lost track of its parent star during its long transit, the object serves as a preserved sample of early interstellar chemistry.
ESA prepares 2029 mission as 3I/ATLAS exits at 50 km/s
To study similar objects in the future, ESA is preparing the Comet Interceptor mission, scheduled for launch in 2029 to wait in a standby orbit and intercept pristine or interstellar comets like 3I/ATLAS. Meanwhile, astronomers continue to compile global data from the current passage for planetary formation studies, calculating that the comet will exit the solar system within a decade at a velocity of 50 km/s. Continuous multi-instrument tracking has filled observation gaps during solar conjunctions and confirmed that the object’s predominant blue glow stems from diatomic carbon (C2) and amidogen (NH2) emissions.
