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Phosphorus (P) is the element with atomic number 15, symbol P. The only common isotope has mass number 31. The unstable isotopes with mass numbers 32 and 33 are created artificially for laboratory use, and natural traces of them do exist, the products of natural radioactivity. Phosphorus is synthesized in oxygen burning, e.g., in late stellar evolution of early stars, and in supernovae.
One compound, phosphine (PH3) attracted attention recently in planetary science when possible detection in Venus's atmosphere was announced, then challenged. A real presence would be considered a possible biosignature because some Earth life produces it in quantities greater than likely to be produced by known abiotic processes.