Interstellar Comet 3I/ATLAS Exhibits Mass Loss and Trajectory Shift Post-Perihelion
Recent observations indicate that interstellar comet 3I/ATLAS has experienced significant mass loss and a slight trajectory change following its closest approach to the Sun.
Interstellar comet 3I/ATLAS, discovered on July 1, 2025, by the Asteroid Terrestrial-impact Last Alert System (ATLAS), has exhibited notable changes following its perihelion on October 29, 2025. Recent observations from October 31 to November 4 indicate that the comet has undergone non-gravitational acceleration, suggesting a slight alteration in its trajectory. This acceleration is attributed to mass loss due to outgassing, a common phenomenon in comets as they approach the Sun.
Harvard astronomer Avi Loeb noted that 3I/ATLAS experienced a radial acceleration away from the Sun of 1.1×10⁻⁶ astronomical units per day squared, and a transverse acceleration of 3.7×10⁻⁷ astronomical units per day squared. These measurements imply that the comet may have lost approximately 13% of its mass near perihelion. Such mass loss is consistent with natural cometary behavior, where heating leads to the vaporization of volatile ices, resulting in outgassing and subsequent acceleration.
3I/ATLAS is the third known interstellar object to pass through our solar system, following 1I/ʻOumuamua and 2I/Borisov. Its unique characteristics, including an anti-tail and unusual brightening near perihelion, continue to intrigue astronomers. Further observations are expected to provide deeper insights into its composition and behavior.