Overview of the MMT 60-Day GEER Experiment on Geologic Samples at Venus Surface Conditions

Laboratory experiments on the behavior of rock and mineral samples under Venus conditions can yield a better understanding of gas-solid chemical weathering on the Venus surface. The Glenn Extreme Environments Rig (GEER) vessel can maintain Venus surface temperature, pressure and a nine-gas atmosphere for months. We provide an overview of the GEER Test Project Marty's Minerals Test (MMT), which ran for 60 days at 460°C, 93 bars under a 9- component Venus-relevant gas mixture. This experiment included over 90 compositionally unique chips and powders of natural samples selected to explore the pathways and relative rates of alteration of a broad range of mineral and rock types. Temperature, pressure, and gas (CO₂, N₂, SO₂, OCS) composition were monitored over the run. Rapid SO₂ depletion from the vessel gas phase occurred throughout the test, indicating sequestration of SO₂ via gas-solid reactions. A significant sink for SO₂ is the formation of iron oxide and nickel sulfide coatings on some chamber parts, which was compensated by multiple SO₂ gas injections during the run. Initial results for selected samples include the formation of secondary minerals at sample surfaces (e.g., on Na₂CO₃, natrite) and complete alteration of other samples (e.g., FeS, troilite) to oxides and sulfides. Some powdered samples consolidated to form hardened layers or chips. These observations show that some mineral phases are chemically and/or physically unstable over the timescale of the run. This test confirms that the GEER is a critical asset and reference point to support the study of gas-solid interactions at Venus conditions.