MEAD CRATER EJECTA: DISTRIBUTION OF EJECTA-DERIVED REGOLITH ON VENUS

Landers on Venus reveal a word largely devoid of regolith. Only a few eolian landforms, indicating abundance regolith, have been identified. Previous work showed that tesserae are capable of preserving impact ejecta (one source of regolith formation) longer than the surrounding low-lying plains. Tesserae cover ~7% of the surface of Venus and appear radar bright owing to their high degree of tectonic deformation. Here, Magellan synthetic aperture radar (SAR) data are analyzed in detail to determine what they reveal about regolith formation in the tesserae. Variations in backscatter coefficient (i.e., radar brightness) on the order of 10s of km are measured to identify ejecta deposits to address whether these variations are associated with post-emplacement processes, such as impact cratering and in-situ erosion, that produce planetary regoliths.

Backscatter coefficient values across 21 tesserae are derived through measurements of backslopes, ridge slopes that face away from the spacecraft during data collection. Lower backscatter coefficient values are suggestive of smoother surfaces at the scale of the emitted energy (Magellan SAR had a 12.6-cm wavelength).

The expected ejecta pattern around Mead crater, the largest impact structure on Venus (~270 km in diameter), was plotted based on measurements of existing parabola ejecta deposits. Three tesserae (Mamitu, Vako-Nana, Tellus) overlap Mead’s expected ejecta parabola deposit. No spatial correlation between backscatter coefficient and expected ejecta pattern was observed. Local variations in backscatter coefficient within other tesserae (e.g., Tellus, Alpha) do correspond to the predicted extent of distal ejecta from complex craters. However, all variations in backscatter coefficient value cannot all be directly attributed to post-emplacement modification processes and may indicate differences in the original tesserae materials.

Though there is tantalizing evidence of significant differences in tesserae materials across Venus, new global mission data, like that proposed by the VERITAS Discovery mission concept, is necessary to address these fundamental questions about our planetary neighbor.