Coupled Gas and Mineral Chemistry in a 60‐Day Venus Weathering Experiment at the Glenn Extreme Environments Rig (GEER)
Alison R. Santos, Mikhail Yu. Zolotov, Martha S. Gilmore, Craig Motil, Kyle Phillips, Valerie TuAbstract
Investigations of the venusian surface suggest chemical alteration (weathering) of rocks in contact with a hot, high‐pressure atmosphere. This alteration was anticipated based on mineral stability considerations and has been supported by laboratory experiments conducted under Venus surface conditions. Here, we exposed iron‐bearing samples (oxides, sulfides, iron‐metal) to a simulated venusian environment (93 bars, 733 K, and a 9‐gas mixture) for 60 days at the NASA Glenn Extreme Environments Rig (GEER). Iron metal, pyrrhotite, and troilite were altered to pyrite and magnetite. Some magnetite formed at the expense of hematite. Neither magnetite nor pyrite was altered. Measured concentrations of CO 2 , SO 2 , and OCS during the run suggest rapid OCS‐SO 2 equilibration and drawdown of sulfur‐bearing gases through reactions with the vessel and sample materials. The observed alteration assemblages and the gas composition in the vessel suggest experimental gas‐phase fugacities ( f O 2 , f S 2 , f SO 2 , f OCS, f CO, f CO 2 ) in the vicinity of the magnetite‐pyrite phase boundary and within the uncertainty of the magnetite‐hematite boundary. Fugacities (log 10 f O 2 of −22.5 to −21.5; log 10 f S 2 of −5.4 to −4.6) and mineralogy in the Fe‐O‐S system are consistent with observation‐based models for the near‐surface conditions on Venus. This experiment supports both gas‐phase chemical equilibrium and equilibration between gases and minerals in the Fe‐O‐S system on the surface of Venus, as proposed six decades ago.