Venus Surface Composition Constrained by Observation and Experiment

• Published in: Space science reviews Vol. 212; no. 3-4; pp. 1511 - 1540
• Main Authors: Gilmore, Martha, Treiman, Allan, Helbert, Jörn, Smrekar, Suzanne
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Netherlands 01.11.2017; Springer Nature B.V
• Subjects: Aerospace Technology and Astronautics; Astrophysics and Astroparticles; Atmosphere; Atmospheric data; Atmospheric models; Basalt; Buffers; Calcite; Carbon dioxide; Emissivity; Experiments; Ferroelectric materials; Hematite; Highlands; Instability; Melts; Mineralogy; Minerals; Oxidation; Petrology; Physics; Physics and Astronomy; Planetology; Radar; Reaction kinetics; Rocks; Silica; Silicon dioxide; Southern Hemisphere; Space Exploration and Astronautics; Space Sciences (including Extraterrestrial Physics; Spacecraft; Spacecraft stability; Sulfur; Sulfur dioxide; Surface stability; Venus; Venus atmosphere; Venus III; Venus surface; Weathering; Geochemistry; Crust; Venus; Mineralogy
• ISSN: 0038-6308; 1572-9672
• DOI: 10.1007/s11214-017-0370-8

New observations from the Venus Express spacecraft as well as theoretical and experimental investigation of Venus analogue materials have advanced our understanding of the petrology of Venus melts and the mineralogy of rocks on the surface. The VIRTIS instrument aboard Venus Express provided a map of the southern hemisphere of Venus at ∼1 μm allowing, for the first time, the definition of surface units in terms of their 1 μm emissivity and derived mineralogy. Tessera terrain has lower emissivity than the presumably basaltic plains, consistent with a more silica-rich or felsic mineralogy. Thermodynamic modeling and experimental production of melts with Venera and Vega starting compositions predict derivative melts that range from mafic to felsic. Large volumes of felsic melts require water and may link the formation of tesserae to the presence of a Venus ocean. Low emissivity rocks may also be produced by atmosphere-surface weathering reactions unlike those seen presently. High 1 μm emissivity values correlate to stratigraphically recent flows and have been used with theoretical and experimental predictions of basalt weathering to identify regions of recent volcanism. The timescale of this volcanism is currently constrained by the weathering of magnetite (higher emissivity) in fresh basalts to hematite (lower emissivity) in Venus’ oxidizing environment. Recent volcanism is corroborated by transient thermal anomalies identified by the VMC instrument aboard Venus Express. The interpretation of all emissivity data depends critically on understanding the composition of surface materials, kinetics of rock weathering and their measurement under Venus conditions. Extended theoretical studies, continued analysis of earlier spacecraft results, new atmospheric data, and measurements of mineral stability under Venus conditions have improved our understanding atmosphere-surface interactions. The calcite-wollastonite CO 2 buffer has been discounted due, among other things, to the rarity of wollastonite and instability of carbonate at the Venus surface. Sulfur in the Venus atmosphere has been shown experimentally to react with Ca in surface minerals to produce anhydrite. The extent of this SO 2 buffer is constrained by the Ca content of surface rocks and sulfur content of the atmosphere, both of which are likely variable, perhaps due to active volcanism. Experimental work on a range of semiconductor and ferroelectric minerals is placing constraints on the cause(s) of Venus’ anomalously radar bright highlands.