According to Mogul and his team, Venus' cloud aerosols contain iron sulfates and sulfuric acid in comparable masses (~ 20% by mass) and three-fold higher abundances of water (~ 60% by mass). This conclusion significantly updates the current perception that the cloud aerosols are composed of highly concentrated sulfuric acid. This also challenges the notion that Venus' atmosphere is dry, where water is extremely limited. Rather, through careful re-analysis of the Pioneer Venus data, the team discovered several lines of evidence supporting a complex aerosol composition containing substantial water and oxidized iron. Their results suggest that the water is bound in hydrates, or water-bearing compounds, such as hydrated ferric sulfate, hydrated magnesium sulfate, and other hydrates.
This new aerosol composition was obtained using data collected over 45 years ago by the Pioneer Venus (PV) Large Probe. While the PV Large Probe descended through Venus' atmosphere towards the surface, several onboard instruments collected data about the atmospheric composition and properties. Among these instruments was the Large Probe Neutral Mass Spectrometer. The dataset collected by this instrument was eventually archived by NASA on microfilm and mostly forgotten about over the following decades by the Venus community.
In 2021, during a conversation about the composition of Venus' clouds, Mogul and Sanjay S. Limaye, a co-author on the article and senior Venus scientist at the University of Wisconsin, Madison, hatched a plan to take a fresh look at the PVLP mass spectral data. Through the networking and persistence of Limaye and Michael J. Way, a NASA scientist and co-author on the study, the archived dataset was uncovered at the NASA Space Science Data Coordinated Archive office and subsequently released online. The team of co-authors on the study was then completed by the addition of Mikhail Yu. Zolotov, a scientist at the Arizona State University who specializes in Venus' geology.
Using evolved gas analysis, the team developed a new understanding of the aerosol composition by re-analyzing the PV Large Probe mass spectra, re-interpretating results from the other PV Large Probe instruments, and re-evaluating results from the Soviet Venera and Vega landers, which also studied Venus' atmosphere. Across these measurements, they found evidence that all of the instruments that sampled within Venus' clouds had inadvertently collected the aerosols and measured their contents.
As the PV Large Probe dropped through Venus' increasingly hot atmosphere, the cloud aerosols collected by the intake inlets, underwent thermal decomposition, and released gases and compounds into the onboard instruments. These gases and compounds included water (H2O), SO2, O2, and likely Fe2O3. Due to the operational workings of the PV Large Probe mass spectrometer, these molecules were identified as as H2O+, SO2+, O2+, and FeO+ in the dataset. Similarly, the Venera and Vega probes carried chemical sensors that measured substantial water in the clouds after the unplanned capture of aerosols.
"Together, these direct measurements in Venus clouds highlight reservoirs of water and iron in the aerosols, and suggest that the iron may arise from the input of cosmic materials," said Mogul. "This type of aerosol composition, which was not previously known, presents new considerations for cloud chemistry models, cloud habitability discussions, and the continued and vigorous exploration of Venus."
Related Links
California State Polytechnic University
Venus Express News and Venusian Science
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