Geology of the V-18 Lachesis Tessera Quadrangle: Evaluating how geologic maps could help us pick landing sites on Venus

Abstract:

An important first step for planning a landed mission on Venus would be to understand the terrain where the lander would set down. The best way to accomplish this is to create a geologic map of the region. As an example, we here present our progress on completing the geologic map of Lachesis Tessera, a quadrangle in the northern hemisphere of Venus (25°-50°N, 300°-330°E). Mapping was based on a 250 m/p Magellan cycle 1 synthetic aperture radar (SAR) 1:5M scale controlled mosaic, but most of the analysis utilized 75 m/p FMAPS. Topographic information was derived from digital elevation models and from gridded elevation data; altimetry data were combined with SAR data to create synthetic stereoscopic images. The V-18 quadrangle includes portions of Sedna and Guinevere Planitiae. There are two ridge belts and embayed fragments of 1-2 possible additional belts, three large central volcanoes, abundant small shield volcanoes and associated flow materials, thirteen impact craters, three named coronae, and several more coronae-like features. A linear grouping of a prominent structural belt, coronae, and coronae-like structures are oriented NW to SE in the southern half of the quadrangle. Important individual structural features include radar-bright lineaments, graben, and wrinkle ridges, as well as broader ridges that may be local folds in regional plains. Several small circular features of with dark interiors or rims but negligible relief have a mysterious origin—possibly a record of craters shallowly buried by regional plains. By mapping out geologic features like these, we will understand more about the questions that a landed mission could answer. Unlike most of Venus, topography data show relatively little relief in this area. Dark materials in radar images of Venus are relatively smooth and thus more likely to meet safety requirements for a landed mission. Regional plains that cover ~80% of the map area include two distinct plains units. The darker plains unit Pr1 is a global unit that is thought to date back to the resurfacing event that covers most of Venus. Landing on this unit would allow us to sample and date these regional plains while still meeting safety requirements. Similarly, landing on one of the anomalous dark circular features would allow us to sample one of the unique features of Venus.