An interstellar comet, 3I/ATLAS, defies expectations with unusual activity and structure, prompting a reevaluation of comet models.

Interstellar object 3I/ATLAS, discovered in July 2025, continues to astonish astronomers as it speeds away from the Sun at over 60 km/s on a retrograde path, approaching Jupiter in March 2026. Unlike typical comets, it exhibits steady, organized outgassing with a persistent, lopsided coma and a stable sunward jet, along with an unusual anti-tail made of large dust grains. Data from NASA’s Parker Solar Probe and other observatories reveal water ice, CO2, hydroxyl, and non-gravitational forces, suggesting complex internal structure or rotation. Its brightness and activity remain strong even at 6.4 AU, indicating a large nucleus and pristine, possibly unique composition. Scientists are reevaluating comet models, with future missions like ESA’s Comet Interceptor expected to explore such objects.