New infrared observations reveal the rare interstellar visitor comet 3I/ATLAS dramatically brightening during its farewell tour of the solar system.

NASA's SPHEREx (Spectro-Photometer for the History of the Universe, Epoch of Reionization and Ices Explorer) space telescope captured views in December 2025 of the comet releasing a surge of gas, dust and complex molecules two months after the object's closest approach to the sun — a surprising outburst that's giving scientists their clearest chemical look yet at material formed around another star, according to a statement from NASA.

The SPHEREx images were taken as the comet was already heading back out of the inner solar system. Instead of fading quietly into the dark, 3I/ATLAS flared with activity, developing a glowing coma rich in water vapor, carbon dioxide and organic compounds. Observations also show a pear-shaped dust tail, created by rocky material being ejected as the comet's activity increases.