Intra-Tessera Plains: Implications of Their Radar Properties for Surface Processes on Venus

Abstract

Intra-tessera plains are radar-dark plains deposits that occur within tesserae. Their emplacement mechanism(s) and composition are poorly constrained, though they are hypothesized to be basaltic lava flows. Here, we map intra-tessera plains within 16 different tesserae spanning various latitudes and elevations. Intra-tessera plains have three dominant geologic units (regional plains, shield plains, and smooth plains) which we compare with morphologically similar lowland plains, and plains that overlap with known parabolic ejecta deposits, to better constrain the ability of these ejecta to modify surface signatures in synthetic aperture radar data. We examine the Magellan radar backscatter, emissivity, and altimetry data of all mapped intra-tessera plains, lowland plains, and parabolic ejecta study regions. Our results support the observation that parabolic ejecta deposits modify the backscatter coefficients of intra-tessera plains and lowland plains by smoothing these materials, while variations in the radar properties caused by differences in plains geologic units are minimal. Conversely, there are clear differences in the backscatter coefficients and emissivity of high- and low-elevation intra-tessera and lowland plains. Our mapped intra-tessera plains follow six different elevation–emissivity patterns. Regardless of which pattern is observed, intra-tessera plains mimic the radar behavior of the tesserae in which they occur. This parallel behavior suggests that the same processes are affecting both terrains, placing constraints on proposed high reflectivity formation mechanisms. While multiple hypotheses remain plausible, our data are most consistent with the atmospheric deposition of metallic frost.