The Direct Mid-infrared Detectability of Habitable-zone Exoplanets around Nearby Stars

Giant planets within the habitable zones of the closest several stars can currently be imaged with ground-based telescopes. Within the next decade, the Extremely Large Telescopes (ELTs) will begin to image the habitable zones of a greater number of nearby stars with much higher sensitivity, potentially imaging exo-Earths around the closest stars. To determine the most promising candidates for observations over the next decade, we establish a theoretical framework for the direct detectability of Earth- to super-Jovian-mass exoplanets in the mid-infrared based on available atmospheric and evolutionary models. Of the 83 closest BAFGK-type stars, we select 37 FGK-type stars within 10 pc and 34 BA-type stars within 30 pc with reliable age constraints. We prioritize targets based on a parametric model of a planet's effective temperature based on a star's luminosity, distance, and age, and on the planet's orbital semimajor axis, radius, and albedo. We then predict the most likely planets to be detectable with current 8 m telescopes and with a 39 m ELT with up to 100 hr of observation per star. Putting this together, we recommend observation times needed for the detection of habitable-zone exoplanets spanning the range from very nearby temperate Earth-sized planets to more distant young giant planets. We then recommend ideal initial targets for current telescopes and the upcoming ELTs.