Date of Graduation

12-2019

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Space & Planetary Sciences (PhD)

Degree Level

Graduate

Department

Space & Planetary Sciences

Advisor/Mentor

Chevrier, Vincent F.

Committee Member

Dixon, John C.

Second Committee Member

Kennefick, Julia D.

Third Committee Member

Potra, Adriana

Keywords

emissivity; experiments; metal sulfides; radar anomaly; reflectivity; Venus

Abstract

Since its detection in the 1960s the source of the unusual radar emissivity signal seen on several highlands on Venus has long eluded researchers. Researchers have determined that a mineral with a high dielectric constant could explain the signal. Using a Venus simulation chamber, we experimentally investigated this enigma to build upon the candidate mineral list that has been compiled over the last several decades. We tested the stability of 8 different minerals and elements at two to three different temperature/pressure regimes in three different gas mixtures meant to simulate the conditions found on Venus for a period of no less than 24 hours. These samples included: Bi/Te/S, Bi2S3/Bi2Te3, Bi2S3/3Te, Pb, PbO, PbS, PbSO4, and Fe7S8. The temperature/pressure regimes simulate the conditions found in the average lowlands, 460°C/95 bar, 4.5 km above the planetary radius, 425°C/75 bar, and 11 km above the planetary radius, 380°C/45 bar. The three tested gases were 100% CO2, 100 ppm of COS in CO2, and 100 ppm of SO2 in CO2. Samples were analyzed via XRD (X-ray Diffraction) and on occasion SEM/EDX (Scanning Electron Microscope/Energy-Dispersive X-ray spectroscopy) or XPS (X-ray Photoelectron Spectroscopy). Additional studies were completed at Okayama University in Japan where we modeled the effect of surface temperature on SO2 abundance and the elevation of the critical altitude (where the emissivity changes) if the source mineral was pyrite (FeS2).

Our Bi/Te/S mixture experiments resulted in the formation of numerous minerals but tetradymite (Bi2Te2S) formed in every tested condition. Our lead experiments revealed that PbS and lead carbonates can form in the highland condition. Pyrrhotite was stable at all tested conditions. Our modeling results verified that surface temperature, SO2 abundance, and the critical altitude are all closely correlated.

The data collected in this project can be used to better understand the near surface environment on Venus. It provides information on the surface-atmosphere reactions that occurs due to the different gases and temperatures/pressures on Venus. Most importantly, our data expands upon the mineral candidate list and identifies which minerals are stable and could perhaps explain the anomalous radar signal.

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