Astronomers have observed remarkable and unexpected behavior from the interstellar comet 3I/ATLAS as it reached perihelion, its closest point to the Sun. Using data collected by NASA’s Solar and Heliospheric Observatory (SOHO) and Solar Terrestrial Relations Observatory (STEREO), scientists reported that the comet not only brightened dramatically but also displayed a mysterious acceleration that cannot be explained by gravity alone.
This finding places 3I/ATLAS alongside a rare class of interstellar visitors and provides valuable clues about materials and forces at work in distant planetary systems beyond our own.
Non-Gravitational Acceleration
According to a detailed analysis led by Harvard astrophysicist Avi Loeb, 3I/ATLAS veered slightly off the trajectory predicted by solar gravitational models. This small but measurable shift – known as non-gravitational acceleration was detected as the comet passed behind the Sun, where spacecraft observations offered the clearest view of its motion.
The acceleration, measured at approximately 3.7 × 10⁻⁶ meters per second squared, was directed away from the Sun. Scientists attribute this to outgassing, a process in which solar heat vaporizes volatile ices within the comet’s nucleus. As these gases escape into space, they act like miniature thrusters, pushing the comet forward much like a natural rocket. The phenomenon confirms that 3I/ATLAS remains active and dynamic, releasing material as it journeys through the inner solar system.
Composition and Brightening
During perihelion on October 29, 2025, when the comet approached within 39.1 million miles of the Sun, it underwent a sudden and intense brightening event. Instruments aboard SOHO detected a rapid surge in luminosity, suggesting a burst of material from the comet’s surface.
Spectroscopic analysis of the surrounding coma revealed an unexpected chemical signature – strong traces of vaporized nickel. Researchers from the European Southern Observatory (ESO) confirmed that nickel gas contributed significantly to the observed brightening. This discovery marks the first confirmed detection of a metallic element in an interstellar object.
Scientists believe that extreme solar heating caused solid nickel grains within the comet to sublimate directly into vapor, a process that has rarely been observed even in native solar system comets. The presence of such metals indicates that 3I/ATLAS likely formed in a metal-rich protoplanetary environment, hinting at a mature and possibly Earth-like stellar system of origin.
Significance and Origin
The detection of both outgassing acceleration and nickel vaporization confirms that 3I/ATLAS is not an inert rock drifting through space but an active comet undergoing complex physical transformations. These findings deepen our understanding of how interstellar bodies behave when exposed to the Sun’s intense radiation and offer a rare glimpse into the composition of other planetary systems.
As 3I/ATLAS continues its outbound journey into deep space, astronomers are closely monitoring it to study how its brightness and trajectory evolve. Each observation brings us closer to uncovering how materials – ranging from ices to metals, survive the long voyage between the stars.
