A detection of phosphine in the atmosphere of a brown dwarf 54 light-years from Earth deepens the mystery of phosphorus chemistry throughout the Milky Way. It's the first and so far only clear detection of phosphine (PH 3 ) in a brown dwarf. The abundance is consistent with what models predict, but this presents a problem: PH 3 's absence in other brown dwarfs. This means there might be something missing in our understanding of phosphorus chemistry, throwing PH 3 's status as a potential biosignature into disarray. "We have some possible clues as to why Wolf 1130C stands out in this respect.