The Mystery Element: Tracing Phosphorus from Stars to Planets*

Phosphorus is a key ingredient for the origin of life, being one of the critical six “NCHOPS” elements. It also is thought to play a role in the formation of rocky planets, and is found in solar system bodes as phosphides or phosphates. Phosphorus is thought to originate in supernovae, yet it remains elusive in the interstellar medium (ISM).  Observations of atomic transitions, the basic avenue for studying the elements in stellar photospheres and the general ISM, are problematic for phosphorus, as its lines lie in obscured regions of the electromagnetic spectrum. Consequently, the abundance of this element has only been measured in a small section of the Galaxy, and in 1% of all planet host stars. Observations of molecules containing phosphorus offer an alternative to characterizing the abundance and distribution of the elements. Here we report new measurements of phosphorus-containing molecules in the ISM, including the detection of PO and PN in molecular clouds at the Galaxy’s edge, and in Orion-KL, the best studied star-forming region. We also describe the current state of phosphorus chemistry in circumstellar envelopes, and present new ALMA images of PO and PN in the outflows of the hypergiant star VY CMa. In addition, new studies of phosphorus and its carriers in meteorite samples will be presented, including those from pristine carbonaceous chondrites. These combined data give insight into the history of phosphorus in the ISM and its possible evolution in protostellar disks and delivery to planet surfaces.