The Direct Mid-Infrared Detectability of Habitable-zone Planets

We establish a theoretical framework for the direct detectability of exoplanets in the mid-infrared based on currently available models. The spectra of temperate (T~300K) exoplanets peak in the mid-infrared, resulting in the maximized contrast to their host star. Compared to previous observations in the near-infrared, this wavelength range enables colder (and hence older) exoplanets to be directly imaged, including habitable-zone planets around nearby stars. Of the 81 closest BAFGK type stars, we select 72 with well-established ages. We then identify the most promising candidates for near-term ground-based observations. We prioritize targets based on a star’s luminosity, age, and the properties of known exoplanets in the system. We then predict the most likely planet types to be detected based on anticipated instrumental sensitivity limits combined with known exoplanet demographics. Putting this together, we recommend observation times needed for the detection of different types of habitable-zone exoplanets, including both mature habitable-zone exoplanets around nearby stars, as well as moderately young giant planets around more distant A-type stars.