Characterizing Proxima b with a mid-infrared nulling spectrograph

As potentially our nearest rocky exoplanet, Proxima b represents a formidable opportunity for exoplanet science and possibly astrobiology. With an angular separation of only 35 mas (or 0.05 AU) from its hosts star, Proxima b is however hardly observable with current imaging telescopes and future space-based coronagraphs. To separate the photons of the planet from those of its hosts star, a solution is to use an interferometer that can easily resolve such spatial scales. In addition, its proximity to Earth and its favorable contrast with its host M dwarf (10^-5 at 10 microns) makes it an ideal target for a space-based nulling interferometer with relatively small apertures. In this talk, we present the main observational challenges to overcome in order to study the atmospheric composition of this planet and review what will be possible with current and/or planned facilities. Then, we describe the concept of a space-based infrared (5-20 microns) interferometer with relatively small apertures (smaller than 1m in diameter) that can measure key details of Proxima b, such as its size, temperature, climate structure, as well as the presence of important atmospheric molecules such as H2O, CO2, O3, NH3, and CH4. Finally, we illustrate the concept by showing realistic observations using synthetic spectra of Proxima b computed with coupled climate chemistry models.