Interstellar Comet 3I/ATLAS Exhibits Unexpected Brightening Near Perihelion
Comet 3I/ATLAS, the third known interstellar object, has shown a rapid increase in brightness as it approached its closest point to the Sun, surprising astronomers.
Comet 3I/ATLAS, the third confirmed interstellar object to traverse our solar system, has exhibited an unexpected surge in brightness as it neared its perihelion on October 29, 2025. This rapid brightening was observed by space-based instruments, including NASA's Solar Terrestrial Relations Observatory (STEREO), the European Space Agency's Solar and Heliospheric Observatory (SOHO), and NOAA's GOES-19 satellite.
The comet's luminosity increased at a rate significantly exceeding that of typical Oort Cloud comets at similar distances from the Sun. Astronomers Karl Battams and Qicheng Zhang noted in a recent study that the cause of this rapid brightening remains unclear. They suggested that factors such as the comet's high velocity—approximately 137,000 mph—and unique nucleus properties, possibly acquired during its interstellar journey, may contribute to this phenomenon.
Observations also revealed that 3I/ATLAS is distinctly bluer than the Sun, indicating that gas emissions contribute substantially to its visible brightness near perihelion. The comet's nucleus is estimated to be between 0.32 to 5.6 kilometers in diameter, with a coma approximately 300,000 kilometers across.
Currently, 3I/ATLAS is positioned behind the Sun from Earth's perspective, rendering it unobservable by ground-based telescopes. It is expected to reappear in the morning sky in early November, allowing for further study. Astronomers anticipate that continued observations will provide more insights into the comet's behavior and composition as it continues its journey through the solar system.