Microwave Emissivity Variations Across Ovda Regio, Venus

Abstract

The surface composition of highland tesserae on Venus critically constrains the geologic and climate history of the planet. We examine one such highland, Ovda Regio, which contains tessera terrain as well as a rare festoon-type volcano, both of which have unknown compositions. Observations of declining surface microwave emission with increasing elevation at Ovda Regio has been attributed to the presence of ferroelectric minerals that undergo a sharp dielectric transition at high elevations. However, there is significant spatial variability in this elevation-dependent emissivity trend. We find that emissivity is lower in the interior of Ovda Regio than in the margins at similar elevations, indicating higher concentrations of ferroelectric minerals in the interior. The lowest emissivity values are associated with the festoon flow and neighboring surfaces, including a morphological unit that drapes over underlying tessera. We hypothesize that the festoon flow eruption produced reactive gasses and tephra that contributed to rapid weathering and formation of abundant ferroelectrics. Modeling the elevation-dependent emissivity behavior demonstrates the presence of ferroelectric minerals with a diffuse, rather than sharp, transition in dielectric properties consistent with relaxor ferroelectrics. These findings indicate that spatial non-uniformity in Ovda Regio's microwave emission is governed by surface modification processes, with the festoon flow eruption leading to the formation of high amounts of ferroelectric minerals. Similar resurfacing processes that occur on other highlands likely regulate regional rates of surface-atmosphere interactions and directly impact present-day surface composition.