Venus' Mass Spectra Show Signs of Disequilibria in the Middle Clouds


Volume 48, Issue 7 e2020GL091327

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).

We re‐examined archived data obtained by the Pioneer Venus Large Probe Neutral Mass Spectrometer (LNMS). Our results reveal the presence of several trace chemical species in Venus' clouds including phosphine, hydrogen sulfide, nitrous acid (nitrite), nitric acid (nitrate), hydrogen cyanide, and possibly ammonia. The presence of these chemicals suggest that Venus' clouds are not at equilibrium; thereby, illuminating the potential for chemistries yet to be discovered. Furthermore, when considering the potential habitability of Venus' clouds, our work reveals a potential signature of anaerobic phosphorus metabolism (phosphine), along with key chemical contributors toward anoxygenic photosynthesis (nitrite) and the terrestrial nitrogen cycle (nitrate, nitrite, possibly ammonia, and N2).

All LNMS data used in this study were obtained from published reports (Hoffman, Hodges, Donahue, et al., 1980; Hoffman, Hodges, Wright, et al., 1980). The LNMS archive data across all altitudes were posted online on October 8, 2020 by the NASA Space Science Data Coordinated Archive (NSSDC) (https://nssdc.gsfc.nasa.gov/nmc/dataset/display.action?id=PSPA-00649).

Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.