New Insights from the James Webb Space Telescope into Interstellar Comet 3I/ATLAS

NASA’s James Webb Space Telescope (JWST) has delivered groundbreaking observations of the interstellar comet 3I/ATLAS, revealing that it is both smaller and far more chemically unusual than scientists initially believed.

A Revised Understanding of Its Size
Early estimates suggested that the nucleus of 3I/ATLAS could measure up to 3.5 miles (5.6 kilometers) in diameter. However, new JWST data, combined with observations from other ground- and space-based telescopes, indicate that the solid nucleus is much smaller—likely under 1 mile (1.6 kilometers) across. The earlier overestimation resulted from confusing the comet’s coma—a dense cloud of gas and dust surrounding the nucleus—with the nucleus itself.

Remarkably Unusual Chemistry
Observations made using JWST’s Near-Infrared Spectrograph (NIRSpec) show that the coma of 3I/ATLAS is extraordinarily rich in carbon dioxide. The measured carbon dioxide–to–water ratio is approximately 8:1, a value about 16 times higher than what is typically seen in comets from our own solar system. This extreme chemical composition suggests that 3I/ATLAS likely formed in a radically different environment—possibly near a carbon dioxide ice line or within a region exposed to intense radiation.

A Rare Window into Cosmic History
Discovered on July 1, 2025, by the ATLAS sky survey, 3I/ATLAS is only the third confirmed interstellar object ever detected passing through our solar system. Traveling at more than 130,000 miles per hour (210,000 kilometers per hour), the comet is expected to reach its closest point to the Sun on October 29, 2025. Its passage provides scientists with an exceptional opportunity to study pristine material that formed before our solar system existed, offering clues about the conditions of the early universe.

As 3I/ATLAS continues its swift journey through the solar system, astronomers worldwide are closely monitoring its motion and composition, hoping to unlock the secrets carried by this ancient visitor from beyond the stars.

Recent Discoveries on Interstellar Comet 3I/ATLAS