When a Comet from Another Star Turns Green: What 3I/ATLAS Is Teaching Us

Imagine looking up during a total lunar eclipse, expecting the moon to turn deep red—and then you notice a faint green glow from a mysterious visitor not from our solar system. That’s exactly what happened with 3I/ATLAS, and its unexpected color shift is opening a window into new comet chemistry and the nature of interstellar visitors. What is 3I/ATLAS and What Has Been Seen So Far 3I/ATLAS is the third confirmed interstellar object (ISO) ever observed, and it’s behaving in ways that are surprising astronomers. Discovered on July 1, 2025, by the survey system ATLAS in Chile, 3I/ATLAS has been...