Locally, Earth has its habitable extremes: Antarctica, the Sahara desert, the Dead Sea, Mount Etna. Globally, our blue planet is positioned in the solar system’s habitable zone, or ‘Goldilocks’ region where the temperature and pressure are just right to support liquid water and life. Across the borders from this goldilocks zone orbit our two neighbors: the runaway greenhouse planet, Venus–which in goldilocks’ terms is ‘too hot’–and the frigid red planet, Mars, which is ‘too cold’.