The comet 3I/ATLAS, detected on July 1, 2025 by the ATLAS telescope in Chile, represents the third interstellar object confirmed in the Solar System. Global astronomers analyze its unusual chemical composition, with elevated carbon dioxide levels surpassing water in the coma, challenging traditional comet formation theories. NASA restricts data disclosure due to budgetary limitations from the U.S. government shutdown, forcing collaborations with the European Space Agency and independent observatories.
This extrasolar origin, identified by its hyperbolic orbit, enables rare studies of processes in distant stellar systems. The object travels at about 220,000 km/h and will reach perihelion on October 30, 2025, at 1.4 astronomical units from the Sun, near Mars’ orbit.
Preliminary data from the James Webb Space Telescope, obtained in August, confirm the presence of carbon monoxide and water vapor, released as hydroxyl detected in ultraviolet light.
- Cometary activity began in May 2025, at 6.4 astronomical units from the Sun.
- Nucleus estimated between 300 meters and 5.6 km in diameter, with over 8% active surface.
- Reddish dust tail, similar to comet 2I/Borisov.
- No ejection bursts or fragmentation observed until October.
Chemical composition defies expectations
Spectroscopic analyses reveal carbon dioxide predominance in the 3I/ATLAS coma, a trait absent in typical Solar System comets. This abundance suggests formation in environments with extreme temperatures and pressures, possibly in outer regions of distant protoplanetary disks.
NASA’s Swift Telescope captured ultraviolet emissions in July and August 2025, indicating water release like a “fire hose” even at cold distances from the Sun. Volatile compounds like carbon monoxide were identified, supporting the hypothesis of prolonged exposure to cosmic radiation during billions of years of interstellar travel.
Collaborations boost observations
Dependence on international partnerships emerged after the shutdown, which paused NASA operations in October. The ESA contributed data from the ExoMars Trace Gas Orbiter, which observed the comet near Mars on October 3, 2025, capturing visible and infrared images.
Observatories in Chile and Europe share orbital telemetry, confirming the hyperbolic trajectory without significant gravitational deviations from nearby stars. This global network enabled reconstructions of 10 million years of the 3I/ATLAS path, identifying 93 close stellar encounters, but none as a likely origin.
The Perseverance rover on Mars recorded images on October 4, showing the comet at 27 million kilometers, with no instrumental anomalies.
Hyperbolic trajectory confirms extrasolar
The 3I/ATLAS orbit follows a hyperbolic pattern, with an entry speed of 245,000 km/h, indicating a single pass through the Solar System. Astronomers used Gaia telescope data to map its galactic path, revealing a “solitary traveler” untouched by recent stellar influences.
In July 2025, Hubble estimated the nucleus as a solid ice coconut with a droplet-shaped dust envelope, 445 million kilometers from Earth. The absence of a prominent water tail, despite activity, points to heat-sensitive volatile ices.
Orbital anomalies spark debates
Scientists recorded an apparent pause in motion relative to background stars in October 2025, near Mars, challenging kinetic expectations. NASA ruled out measurement errors, attributing it to subtle core vibrations detected by spectroscopy.
This immobility lasted days without observed energy loss, leading to revisions in celestial mechanics models for interstellar objects. Nordic Optical Telescope observations in July confirmed diffuse coma and reddish color, indicative of organic dust.
The comet resumed acceleration toward perihelion, with predicted passages by Venus in November 2025 and Jupiter in March 2026.
Continuous monitoring demands resources
Ground telescopes track 3I/ATLAS until September 2025, before the solar conjunction on October 21, which will block visibility. It will reappear in December, with apparent magnitude above 12, visible only to professional equipment.
Collaboration with missions like SPHEREx and TESS provided early activity data, measuring emissions at 1420 MHz in the hydrogen line, with no random patterns detected. These efforts highlight the need for sustained astronomy investments to capture rare visitors.
The object represents a “message from another planetary system,” with potential for insights into interstellar chemistry and distant world formation.