Super-Earths and Earth-like Exoplanets

In the last few years astronomical surveys have expanded the reach ofplanetary science into the realm of small and dense extrasolar worlds. Theseshare a number of characteristics with the terrestrial and icy planetaryobjects of the Solar System, but keep stretching previous understanding of theknown limits of planetary thermodynamics, material properties, and climateregimes. Improved compositional and thermal constraints on exoplanets below∼2 Earth radii suggest efficient accretion of atmosphere-forming volatileelements in a fraction of planetary systems, pointing to rapid formation,planet-scale melting, and chemical equilibration between the core, mantle, andatmosphere of rocky and volatile-rich exoplanets. Meaningful interpretation ofnovel observational data from these worlds necessitates cross-disciplinaryexpansion of known material properties under extreme thermodynamic, non-solarconditions, and accounting for dynamic feedbacks between interior andatmospheric processes. Exploration of the atmosphere and surface composition ofindividual, short-period super-Earths in the next few years will enable keyinferences on magma ocean dynamics, the redox state of rocky planetary mantles,and mixing between volatile and refractory phases in planetary regimes that areabsent from the present-day Solar System, and reminiscent of the conditions ofthe prebiotic Earth. The atmospheric characterization of climate diversity andthe statistical search for biosignatures on terrestrial exoplanets on temperateorbits will require space-based direct imaging surveys, capable of resolvingemission features of major and trace gases in both shortwave and mid-infraredwavelengths.