Possible Forms of Phosphorus in the Venus Cloud Deck

The recent report of phosphine (PH₃) in the Venusian cloud deck near 56 km altitude¹ has raised interest in photo- and thermo-chemical processes involving phosphorus that may be occurring in the clouds and atmosphere. The source of atmospheric phosphorus is likely to be volcanic emissions. Oxidation processes are expected to result in a variety of phosphorus oxides. In the clouds, such oxides are liquids or solids. PH₃ encountering sulfuric acid cloud aerosols should produce phosphorous acid and phosphoric acid (H₃PO₃ and H₃PO₄, respectively). More complex species, such as pyrophosphoric acid (H₄P₂O₇) may also be created. PH₃ can be regenerated by the combination of four phosphorous acids transforming forming by disproportionation into three phosphoric acid molecules and a single phosphine molecule. As many of the forms of phosphorus species in the cloud deck are non-gaseous, determining their abundances and relevant chemical formation processes would require in-situ mass spectrometric measurements via an in-strument capable of vaporizing the liquid and solid aerosols and then measuring the resulting gases.

¹Greaves, J. S. et al.. 2020. Nature Astronomy doi.org/10.1038/s41550-020-1174-4.