Low radar emissivity signatures on Venus volcanoes and coronae: New insights on relative composition and age

Abstract

Multiple studies reveal that most of Venus highlands exhibit anomalously high radar reflectivity and low radar emissivity relative to the lowlands. This phenomenon is thought to be the result of atmosphere-surface interactions in the highlands, due to lower temperatures. These reactions are a function of rock composition, atmospheric composition, and degree of weathering. We examine the Magellan radar emissivity, altimetry and SAR data for all major volcanoes and coronae on Venus. We characterize and classify edifices according to the pattern of the variation of radar emissivity with altitude. The volcanic highlands can be classified into 7 distinct patterns of emissivity that correspond to at least 3 discrete types of mineralogy based on the altitude (temperature) of the emissivity anomalies. The majority of emissivity anomalies support the hypothesis of a weathering phenomenon at high altitude (>6053 km), but we also find strong emissivity anomalies at lower altitudes that correspond spatially to individual lava flows, indicating variations in mineralogy within an evolving volcanic system. The emissivity signature of tallest volcanoes on Venus are consistent with the presence of ferroelectric minerals in their rocks, while volcanic edifices in western Ishtar Terra and eastern Aphrodite Terra are consistent with the presence of semiconductor minerals. Sapas Mons and Pavlova Corona are also consistent with ferroelectrics, but at a different Curie temperature than the other volcanoes in Atla Regio. The spatial distribution of radar emissivity classes correlates to different geologic settings indicating that different mantle source regions (deep/shallow plumes, and possible convergence zones) may contribute to differences in mineralogy for the studied edifices. Finally, we show that the emissivity signatures of Idunn, Maat and other volcanic edifices are consistent with relatively fresh and unweathered rocks, indicating recent or possibly current volcanism on Venus.