Astronomers have captured a spectacular image showing the tail of interstellar intruder comet 3I/ATLAS beginning to grow. The photo was taken on August 27, 2025, using the Gemini South telescope on Cerro Pachon in Chile, operated by a team of scientists and students.
3I/ATLAS was discovered on July 1 by the ATLAS (Asteroid Terrestrial-impact Last Alert System) system. It is only the third object ever found in our solar system that is believed to have originated from around another star. The previous two interstellar “guests” were the cigar-shaped Oumuamua, discovered in 2017, and the comet-asteroid hybrid 2I/Borisov, discovered in 2019.
All of these objects offer scientists a unique opportunity to study material from another planetary system. And 3I/ATLAS’s growing tail provides a fascinating insight into the comet’s composition. But this opportunity is short-lived: like ‘Oumuamua and 2I/Borisov, this comet will eventually leave the solar system. When such comets approach the Sun, solar radiation heats their ice, which immediately evaporates, bypassing the liquid phase. This process is called “sublimation.” This gas erupts from the comet, forming its famous “coma” and tail. The closer a comet approaches the Sun, the greater the intensity of evaporation, and the longer its tail becomes.
