  Proxima b is our nearest potentially rocky exoplanet and represents a
formidable opportunity for exoplanet science and possibly astrobiology. With an
angular separation of only 35~mas (or 0.05~AU) from its host star, Proxima b is
however hardly observable with current imaging telescopes and future
space-based coronagraphs. One way to separate the photons of the planet from
those of its host star is to use an interferometer that can easily resolve such
spatial scales. In addition, its proximity to Earth and its favorable contrast
ratio compared with its host M dwarf (approximately 10$^{-5}$ at 10 microns)
makes it an ideal target for a space-based nulling interferometer with
relatively small apertures. In this paper, we present the motivation for
observing this planet in the mid-infrared (5-20 microns) and the corresponding
technological challenges. Then, we describe the concept of a space-based
infrared interferometer with relatively small ($<$1m in diameter) apertures
that can measure key details of Proxima b, such as its size, temperature,
climate structure, as well as the presence of important atmospheric molecules
such as H$_2$O, CO$_2$, O$_3$, and CH$_4$. Finally, we illustrate the concept
by showing realistic observations using synthetic spectra of Proxima b computed
with coupled climate chemistry models.
