The comet 3I/ATLAS has reached its closest point to the Sun, revealing significant findings regarding its chemical composition. Observations from the Gemini South Telescope in late October showed that the comet”s tail expanded to 30 arcseconds, approximately 56,000 kilometers, exhibiting increased structural complexity.
Intensified outgassing has been observed, with the comet ejecting hydroxyl radicals and cyanogen, as reported by the Neil Gehrels Swift Observatory. Its trajectory remained stable, traveling at a speed of 68 kilometers per second without any deviations.
Data from the James Webb Space Telescope confirmed a coma dominated by carbon dioxide, with an 8:1 CO2-to-water ratio that is six times higher than the norm typically found in the solar system. Additionally, traces of nickel vapor and carbon monoxide were detected at distances greater than 6 astronomical units (AU), indicating that the comet likely formed in a cold, distant protoplanetary disk.
These observations suggest that 3I/ATLAS is over 10 billion years old, predating the formation of the Sun. The detection of sulfur and iron further differentiates it from other comets, such as 2I/Borisov.
Upcoming missions are set to observe the comet closely. NASA”s Europa Clipper is expected to cross the comet”s ion tail between October 30 and November 6, while the European Space Agency”s JUICE mission will conduct observations on November 3 from a distance of 97 million kilometers from Venus, utilizing spectrometers for particle analysis. Data from Mars orbiters, including MAVEN and ExoMars TGO, was gathered during a flyby on October 3, when the spacecraft was 28 million kilometers distant.
The Solar and Heliospheric Observatory“s LASCO C2 coronagraph tracked the comet from October 18 to October 24, reaching down to a magnitude of 12. An image captured by Hubble on July 21 displayed a droplet-shaped nucleus under 1 kilometer in size, surrounded by a reddish coma due to dust particles.
Additional observations were made by the GOES-19 weather satellite and the PUNCH mission, which provided faint images near conjunction. Amateur astronomers in southern locations have documented jets from the comet that appear to be directed toward the Sun, which is unusual for typical tail geometry.
Research efforts spanning multiple wavelengths have contributed to mapping interstellar material relevant for future exoplanet formation models. The comet”s eccentric orbit, with an eccentricity of approximately 6, guarantees that it will exit the solar system without being gravitationally bound to the Sun.
The closest approach to Earth is anticipated on December 19, 2025, at a distance of 1.8 AU, or about 270 million kilometers, which poses no threat to our planet. Visibility is expected to improve in early December when the comet will be located in the constellation Virgo, displaying a magnitude between 10 and 12, making it observable with binoculars or small telescopes.
Post-perihelion heating has been measured at 770 watts per square meter, raising questions about the structural integrity of the comet. So far, there have been no reports of fragmentation. The International Asteroid Warning Network will initiate a special exercise from November 27, 2025, to January 27, 2026, focusing on comet astrometry, which will require codes from the Minor Planet Center and a workshop scheduled before November 7. This annual drill was chosen for 3I/ATLAS in light of recent interest, aiming to enhance orbital measurements.
Jet activity directed towards the Sun and the comet”s alignment with the ecliptic have prompted further reviews, although NASA attributes these observations to natural dynamics. Astrophysicist Avi Loeb has noted the potential for technosignatures, but current data aligns with expected cometary behavior. No radio signals or maneuvers have been detected, consistent with predictions. The comet”s mass, estimated to be 10^6 times greater than that of “Oumuamua, aids in calculating its density based on a mass loss of two million tons since its discovery.
