For millions of years, a fragment of ice and dust drifted through interstellar space, its origin, a distant planetary system. This summer, that fragment finally entered our Solar System, becoming only the third confirmed interstellar visitor and earning the designation 3I/ATLAS. When astronomers at Auburn University pointed NASA's Swift Observatory toward this icy chunk, they detected water vapour streaming from its surface. It was revealed through the faint ultraviolet glow of hydroxyl molecules and was completely unexpected.