NASA's SPHEREx space telescope witnessed an extraordinary event in December 2025: the interstellar comet 3I/ATLAS flaring up as it bid farewell to our solar system. This rare occurrence provided scientists with a unique opportunity to study material formed around another star, offering a chemical glimpse into the comet's composition. The comet, discovered in July 2025 by the ATLAS asteroid survey, is only the third interstellar object spotted passing through our solar system, following 1I/'Oumuamua in 2017 and 2I/Borisov in 2019. However, 3I/ATLAS stood out with its prolonged chemical display, which SPHEREx was perfectly positioned to observe. SPHEREx, an infrared space telescope, revealed not just dust but a diverse array of molecules streaming from the comet, including water ice, carbon dioxide, methane, methanol, and cyanide, all essential components for planetary formation. The comet's activity intensified well after perihelion, suggesting that sunlight gradually penetrated beneath its surface, triggering a delayed release of ancient ices. This discovery offers a rare chance to compare our local comets with icy bodies formed around other stars, potentially revealing the prevalence of planetary and life-forming raw materials throughout the Milky Way.
