Comet 3I/ATLAS Reveals CO2-Rich Composition, Unveiling Cosmic Mysteries

A remarkable interstellar visitor, Comet 3I/ATLAS, has unveiled secrets that could transform our understanding of distant star systems. After its closest approach to Earth, this comet has provided an unprecedented view of its chemical makeup, revealing a composition rich in carbon dioxide (CO2). This discovery offers insights into materials that formed around a different star, enhancing our knowledge of planetary formation across the universe.

Discovered by NASA’s ATLAS survey telescope in Chile, Comet 3I/ATLAS is only the third confirmed interstellar object to enter our solar system. Its trajectory, which exceeds 57 km/s, ensures it will not remain bound to the Sun, making its passage a rare opportunity for scientific study. The James Webb Space Telescope (JWST) played a crucial role in this investigation, detecting a pronounced CO2 signature that indicates a significant difference from typical solar system comets, which tend to be water-rich.

Insights into Extrasolar Material

The CO2-rich coma of 3I/ATLAS serves as a rare sample of extrasolar material. By analysing its unique chemical fingerprint, astronomers can infer the conditions present in the comet’s home star system. This information could refine models of planetary formation, especially concerning the distribution of volatile compounds essential for the emergence of life.

NASA’s Europa Clipper mission contributed further insights by capturing a distinctive ultraviolet perspective of the comet using its Ultraviolet Spectrograph (Europa-UVS). This view was made possible when Earth and Mars observations were limited. Researchers noted that Europa-UVS “can detect fundamental transitions that show gas release and molecular breakup.” This capability allowed scientists to observe gases escaping from the comet and monitor the breakdown of water molecules into hydrogen and oxygen atoms.

The ultraviolet measurements facilitated mapping of the comet’s dust and plasma tails from an unusual angle, revealing outgassing patterns shortly after its perihelion. The data also provided insights into the speed and density of the ejected gases, which appear to interact strongly with solar radiation.

Collaborative Observations Enhance Understanding

The European Space Agency’s (ESA) JUICE mission, which is equipped with complementary ultraviolet capabilities, is expected to aid in reconstructing the comet’s tail structure in three dimensions. This analysis will further illuminate the comet’s activity and reveal new clues about the forces shaping interstellar comets.

Observing 3I/ATLAS from Earth presented challenges, especially as the comet approached the Sun. NASA’s Parker Solar Probe filled this observational gap by capturing daily images from October 18 to November 5, 2025. The probe’s WISPR camera successfully navigated the Sun’s intense glare to track the comet’s tail and dust emissions. According to NASA, these images provide a critical time series during a period when ground-based tracking was impossible, offering unprecedented insight into the comet’s behaviour near perihelion.

The complex manoeuvres of the spacecraft, combined with sophisticated image processing, allowed researchers to filter out coronal brightness. The resulting data reveal how the comet’s dust and gas interact with solar wind, providing a rare window into processes that may be common in other star systems but are seldom observable in real time.

X-ray observatories added another layer to this extensive study. ESA’s XMM-Newton observed 3I/ATLAS on December 3, 2025, followed by Japan’s XRISM mission from November 26 to 28. These observations documented X-ray emissions extending hundreds of thousands of kilometres from the comet’s nucleus, indicating interactions between solar-wind ions and neutral gases in the coma.

For amateur astronomers, Comet 3I/ATLAS remains a telescope-only target, with an estimated magnitude of 12.8 and currently positioned near the constellation Leo. Although faint, it continues to offer significant scientific value. Its passage also emphasizes the importance of international cooperation in space exploration, as data from multiple spacecraft and observatories combine to create a comprehensive picture of this unique interstellar visitor.