Supplementary Files for "Overview of the MMT 60-day GEER Experiment on Geologic Samples at Venus Surface Conditions" by Gilmore et al.

The present day Venus lowlands lie at a temperature of ~450-460°C and pressure of ~90-96 bars, under a supercritical CO₂ atmosphere containing a mix of S-bearing gases. Laboratory experiments on the behavior of rock and mineral samples under these conditions can yield a better understanding of gas-solid chemical weathering on Venus. The Glenn Extreme Environments Rig (GEER) vessel can maintain Venus’ surface temperature, pressure and a nine-gas atmosphere for months. Here, 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 includes over 90 compositionally unique chips and powders of natural geologic samples, selected to explore the style and relative rates of alteration of a broad range of mineral and rock types. Target 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 consumption of this gas by gas-solid reactions. A significant sink for SO₂ is the formation of iron oxide and Ni 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 Na₂CO_3,natrite) and complete alteration of samples to secondary oxide and sulfide phases (e.g., FeS, troilite), consistent with the reaction of minerals with S-bearing gases within the chamber. Some 20-45 µm powdered samples consolidated to form hardened layers or chips during the test. These observations show that some mineral phases are chemically and/or physically unstable over rapid time scales at test conditions. Transportation of redeposition of fine (20-45 µm) grains occured within some individual crucibles that lay in front of the gas inlet valve, indicating gas speeds of  >1 m/s within this region of the chamber. Samples, their containers, and the stainless steel vessel parts darkened to varying degrees after the test, which can be ascribed to: 1) deposition of fine carbon-bearing compounds, sulfide, and metallic particles, 2) mineral breakdown and/or 3) production of secondary minerals via reaction. This test confirms that GEER is a critical asset and reference point to support the study of gas-solid interactions on the surface of Venus.