We present a re-examination of mass spectral data obtained from the
Pioneer Venus Large Probe Neutral Mass Spectrometer. Our interpretations
of differing trace chemical species are suggestive of redox
disequilibria in Venus’ middle clouds. Assignments to the data (at 51.3
km) include phosphine, hydrogen sulfide, nitrous acid, nitric acid,
carbon monoxide, hydrochloric acid, hydrogen cyanide, ethane, and
potentially ammonia, chlorous acid, and several tentative PxOy species.
All parent ions were predicated upon assignment of corresponding
fragmentation products, isotopologues, and atomic species. The data
reveal parent ions at varying oxidation states, implying the presence of
reducing power in the clouds, and illuminating the potential for
chemistries yet to be discovered. When considering the hypothetical
habitability of Venus’ clouds, the assignments reveal a potential
signature of anaerobic phosphorus metabolism (phosphine), an electron
donor for anoxygenic photosynthesis (nitrite), and major constituents of
the nitrogen cycle (nitrate, nitrite, ammonia, and N2).