Major International Effort Reveals Secrets of Interstellar Comet

A global collaboration of astronomers has unveiled new images and chemical data regarding the interstellar comet 3I/ATLAS. This information highlights its nucleus size and distinctive gas composition as it departs from our solar system. Observations made by the Hubble Space Telescope and the James Webb Space Telescope indicate that the comet’s nucleus measures approximately 2.6 kilometres in diameter. Notably, the comet’s gas coma contains methane, carbon dioxide, and water, marking the first direct detection of methane in an object known to originate outside our solar system.

First identified on July 1, 2025, by the Asteroid Terrestrial-impact Last Alert System (ATLAS) in Chile, 3I/ATLAS is only the third recognized interstellar object to enter our solar system, following the cigar-shaped ‘Oumuamua and Comet Borisov. Unlike its predecessors, which appeared to pass through silently, 3I/ATLAS has provided a wealth of data, enabling astronomers to closely monitor its activity.

What sets this comet apart is its hyperbolic trajectory, suggesting it is moving too quickly for the Sun to capture it. At its closest approach, or perihelion, in October 2025, it reached speeds of approximately 68.3 km/s. By early February 2026, data from both the Hubble and James Webb telescopes confirmed the unprecedented detection of methane, offering a chemical profile of a distant planetary system billions of miles away.

The robust methane outgassing observed during late 2025 and January 2026 presents a unique data profile that distinguishes 3I/ATLAS from native solar system comets. This suggests that the building blocks of planets in other galaxies may not differ significantly from those in our own, although the comet’s behavior implies a chaotic home system.

The scale of the observational effort has been considerable, with telescopes positioned from the Atacama Desert in Chile to the high altitudes of Hawaii’s Mauna Kea, working in tandem to study 3I/ATLAS. Instruments on various NASA missions, including MAVEN, TESS, and the Mars Reconnaissance Orbiter, have provided insights into the comet’s coma and tail throughout its journey. Additionally, the SPHEREx mission has monitored changes in the comet’s coma, noting significant amounts of carbon dioxide and water ice as it released gas and dust during its approach to the Sun.

Adaptive optics techniques have helped researchers overcome the atmospheric disturbances that often obscure observations from Earth. This has allowed for more precise measurements of the nucleus, confirming its effective diameter of approximately 2.6 kilometres. Scientists believe that 3I/ATLAS is less dense and more porous than typical comets, resembling a loosely packed snowball of interstellar material.

The scientific community recognizes an irony in the fact that insights into a foreign star system may come from this single interstellar object, providing more information than decades of observations of distant planets. As researchers analyze the comet, they have noted an unusual abundance of carbon dioxide relative to water, along with the surprising detection of nickel vapor earlier in its journey.

Currently, 3I/ATLAS is on an outbound trajectory toward the outer solar system. Continuous monitoring will occur as the comet’s activity diminishes. Some estimates suggest that this interstellar traveler could be as much as three billion years older than our own 4.6 billion-year-old solar system, with some researchers positing an age of up to seven billion years. This comet serves as a time capsule, representing the remnants of a world that may have existed long before Earth formed.

As 3I/ATLAS continues its journey, it is expected to pass by Jupiter in March 2026, marking the final leg of its passage through our solar system. This remarkable interstellar visitor is leaving behind valuable data that will contribute to our understanding of the universe and the processes that shape planetary systems.