CLASSIFICAITON OF VENUSIAN TESSERAE FROM MAGELLAN SURFACE ROUGHNESS CHARACTERISTICS (Invited Presentation)

Tesserae represent some of the most ancient materials on Venus and, as such, preserve the longest record surface evolution on the planet. This is particularly exciting if Venus had a much different climate in its past that was recorded by these ancient rocks. To get at this question, researchers have used Magellan synthetic aperture radar (SAR), topography and emissivity datasets to characterize tesserae, identified as radar-bright materials with at least two intersecting sets of tectonic structures. Here, we analyze Magellan SAR data to explore the statistical distribution of radar backscatter coefficient values to draw conclusions about the diversity of Venusian tesserae.

SAR left-look data from the Magellan mission were used to derive backscatter coefficient for 22 tesserae distributed latitudinally and longitudinally across Venus. Data were extracted from near the crestline of away-facing (east-facing) ridge slopes.

There is significant variability in the backscatter coefficient values of the mapped tesserae, with backscatter range from approximately -30 dB to 13 dB. Average backscatter behaviors suggest that the variations observed between tesserae are relatively small, with a total range in average backscatter of only ~6 dB. The largest backscatter values tended to be associated with tesserae at high elevations, above the “snow line” or ~6053 km planetary radius. Impact crater ejecta have a strong effect on backscatter coefficients, decreasing backscatter values by ~2.5 dB.

Measured backscatter coefficient distributions in the tesserae are significant and imply real differences between these deposits. Removing high emissivity materials and impact crater ejecta results in a narrow range in backscatter values. Though small variations are still statistically significant. Remaining backscatter coefficient values are used to divide tesserae into two groups: deposits that are smoother than average tesserae and those that are rougher than average. This result presents a different framework to assess tesserae and provides groupings that are distinct from other analyses of Magellan data. Current results indicate that upcoming missions will have to consider the presence of crater ejecta and other transported sediments when evaluating the rock types and diversity of tesserae.