A Technology and Science Gap List for Habitable-Zone Exoplanet Imaging with Ground-Based Extremely Large Telescopes

The Pathways to Discovery in Astronomy and Astrophysics for the 2020s decadal survey highlighted the ability of the coming generation of 30-meter-class telescopes "to detect, image, and characterize temperate rocky planets around low-mass stars, measure their atmospheric compositions including searches for oxygen." However, many of the technologies required to reach the challenging contrast ratios associated with this science case are not yet available, and targeted preparatory science must be carried out well in advance of these observations. In this paper, we draw from the example of NASA's Exoplanet Exploration Program and propose a preliminary version of a "Technology Gap List" and "Science Gap List" for the ground-based imaging of rocky planets around the nearest stars with extremely large ground-based telescopes. These lists can be used to prioritize precursor technical demonstrations and observations with current and near-term high contrast instrumentation, so that the community is ready to exploit the collecting area of extremely large telescopes.