¹J. Brossier,¹M.S. Gilmore,¹K. Toner,¹A.J. Stein
Journal of Geophysical Research, Planets (in Press) Link to Article [https://doi.org/10.1029/2020JE006722]
¹Wesleyan University, Department of Earth and Environmental Sciences, Planetary Sciences Group, 265 Church Street, Middletown, CT, 06459 USA
Published by arrangement with John Wiley & Sons

NASA’s Magellan mission revealed that many Venus highlands exhibit low radar emissivity values at higher altitudes. This phenomenon is ascribed to the presence of minerals having high dielectric constants, produced or stabilized by temperature‐dependent chemical weathering between the rocks and the atmosphere. Some large volcanoes on Venus have multiple reductions of radar emissivity at varying altitudes. We present morphological maps of major lava flow units at Maat, Ozza and Sapas montes and compare them to radar emissivity. Sapas has a single reduction in emissivity values at 6054.6 km, while Maat and Ozza have several reductions at altitudes of 6052.5–6056.7 km. Emissivity values are highly spatially correlated to individual lava flows indicating that minerals in the rocks control the emissivity signature. The emissivity patterns at these volcanoes require at least 4 individual ferroelectric mineral compositions in the rocks that are highly conductive at Curie temperatures of 693–731 K. These temperatures are compatible with chlorapatite and some perovskite oxides. Modeling the minimum volumes of ferroelectrics (10s–100s ppm) shows the volume and type of ferroelectric may vary over the lifetime of a single volcano. The modeled volumes of ferroelectrics in Ozza and Sapas are greater than in Maat, consistent with the production of ferroelectrics via weathering over a longer period of time, and supporting the idea that Maat has younger volcanic activity. The stratigraphic relationship of Maat’s youngest flows with impact craters may indicate the timeframe of the production of specific ferroelectrics via chemical weathering is over 9–60 Ma.

¹Romain Tartèsea,²Paolo A. Sossi,³Frédéric Moynier
Proceedings of the National Academy of Sciences of teh United States of America (PNAS) (in Press) Link to Article [DOI: https://doi.org/10.1073/pnas.2023023118]
¹Department of Earth and Environmental Sciences, The University of Manchester, M13 9PL Manchester, United Kingdom;
²Institute of Geochemistry and Petrology, ETH Zürich, CH-8092 Zürich, Switzerland;
³Université de Paris, Institut de Physique du Globe de Paris, CNRS UMR 7154, 75005 Paris, France

Rocks from the lunar interior are depleted in moderately volatile elements (MVEs) compared to terrestrial rocks. Most MVEs are also enriched in their heavier isotopes compared to those in terrestrial rocks. Such elemental depletion and heavy isotope enrichments have been attributed to liquid–vapor exchange and vapor loss from the protolunar disk, incomplete accretion of MVEs during condensation of the Moon, and degassing of MVEs during lunar magma ocean crystallization. New Monte Carlo simulation results suggest that the lunar MVE depletion is consistent with evaporative loss at 1,670 ± 129 K and an oxygen fugacity +2.3 ± 2.1 log units above the fayalite-magnetite-quartz buffer. Here, we propose that these chemical and isotopic features could have resulted from the formation of the putative Procellarum basin early in the Moon’s history, during which nearside magma ocean melts would have been exposed at the surface, allowing equilibration with any primitive atmosphere together with MVE loss and isotopic fractionation.