3I/ATLAS created quite the buzz as it flew through our Solar System. As just the third interstellar object (ISO) ever detected, what our instruments observed as it approached our Sun and began heading back to deep space provided tantalizing clues about the star system in which it formed. In particular, new observations from the Atacama Large Millimeter/submillimeter Array (ALMA) have yielded the first-ever measurement of deuterated water (or "semi-heavy water") in an ISO. The discovery provides a chemical window into the cold conditions that characterize its home star system. The research was led by PhD student Luis E. Salazar Manzano, a PhD student at the University of Michigan, and assistant professor Teresa Paneque-Carreño, the Principal Investigator of the ALMA Director's Discretionary Time program that made the discovery.…