Venus as an anchor point for planetary habitability

A major focus of the planetary science and astrobiology community is understanding planetary habitability, including the myriad factors that control the evolution and sustainability of temperate surface environments such as that of Earth. The few substantial terrestrial planetary atmospheres within the Solar System serve as a critical resource for studying these habitability factors, from which models can be constructed for application to extrasolar planets. The recent astronomy and astrophysics and planetary science and astrobiology decadal surveys both emphasize the need for an improved understanding of planetary habitability as an essential goal within the context of astrobiology. The divergence in climate evolution of Venus and Earth provides a major accessible basis for understanding how the habitability of large rocky worlds evolves with time and what conditions limit the boundaries of habitability. Here we argue that Venus can be considered an `anchor point' for understanding planetary habitability within the context of the evolution of terrestrial planets. We discuss the major factors that have influenced the respective evolutionary pathways of Venus and Earth, how these factors might be weighted in their overall influence and the measurements that will shed further light on their impacts on these worlds' histories. We further discuss the importance of Venus with respect to both the recent decadal surveys and how these community consensus reports can help shape the exploration of Venus in the coming decades.