Exploring Venus subsurface: Analysis of geological targets and their properties

The exploration of Venus is increasingly gaining importance in the planetary science community. Recently, EnVision has been selected as the European Space Agency's fifth Medium-class mission with a launch targeted in 2030. The subsurface radar sounder (SRS) instrument on board EnVision aims at profiling the shallow crust of Venus. The current phase of development of SRS focuses on a detailed performance analysis based on 3D sim-ulations of the expected subsurface scenarios. This requires inputs on the composition, roughness, location and geometry of the geological features. However, the high uncertainty in the current knowledge of Venus due to the lack of high-quality data implies that several hypotheses exist for these inputs. The goal of this paper is to identify these hypotheses from the perspective of the scientific objectives of subsurface exploration of Venus' shallow crust. In this context, we identify geological features (a.k.a. targets) that are likely to be associated with sub-surface dielectric interfaces. For each target, we review the literature for information on the simulation inputs, analogs of the targets (with possible detection by past radar sounders on other planetary bodies), expected subsurface models representing different hypotheses and the potential role of SRS data in resolving the ambi-guities. The material presented here will be critical to support future activities on detailed performance assess-ment and radar sounder simulations. We also present a map of the potential targets for subsurface sounding, which can support operations planning of SRS.