Surficial Deposits and Access to Materials with Known Geological Context

Introduction: Landing on Venus and geochemical investigations of Venusian materials either in-situ or with returned samples are thought to be of the highest priority in future scientific robotic exploration of Ve-nus. Harsh conditions at the surface strongly limit mobility and operations at the landing sites, as well as the total number of different samples that can be analyzed. This makes it especially important that the samples are taken from known and pre-planned geological situation ; for example, it would be desirable to understand, how to reliably get unaltered igneous material, altered material form a known source, etc. This is not easy, because remote sensing of Venusian surface is principally limited due to thick layer of clouds. Here I summarize relevant current knowledge on Venusian surface layer and apply it to analysis of accessibility of materials with known geological context. I consider here typical terrains in the vast Venusian plains and do not consider the exotic materials at high elevations. Volcanic units seen in SAR images. Information about geology and surface properties has been obtained mostly with microwave remote sensing techniques. Imaging with the synthetic-aperture radar (SAR) on the Venera-15,-16 Venus orbiters, then from the Earth with the Arecibo radar facility, and, finally, by the Magellan orbiter has revealed a spectacular surface dominated by extensive volcanic deposits and deformed by abundant tectonic features. The generally pristine appearance of the volcanic morphologies indicates a very low rate of exogenic resurfacing during the recent half-a-billion years long geologic history. This pristine morphology gives a good chance that the original volcanic material is preserved, but it would be wrong to assume that it is accessible immediately at the surface. The sharp lava flows outlines seen as pristine morphology in the SAR images (the best resolution is ~200 m) can be preserved even if the original flow surface is heavily reworked or covered by meters of secondary surficial deposits. A number of lines of evidence show that this is the case in many locations on the planet. Dust deposits: There are about a thousand of impact craters on Venus. Impact process inevitably produces at least some fine dust, which was inevitably suspended in the dense atmosphere and could be redistributed and deposited regionally or globally. Such dust can contaminate the surface with altered materials from distal sources. Thin (a centimeter or thinner) dust does not have any unique signature in the microwave remote sensing data. …