  JWST promises to be the most versatile infrared observatory for the next two
decades. The Near Infrared and Slitless Spectrograph (NIRISS) instrument, when
used in the Aperture Masking Interferometry (AMI) mode, will provide an
unparalleled combination of angular resolution and sensitivity compared to any
existing observatory at mid-infrared wavelengths. Using simulated observations
in conjunction with evolutionary models, we present the capability of this mode
to image planetary mass companions around nearby stars at small orbital
separations near the circumstellar water frost-line for members of the young,
kinematic moving groups Beta Pictoris, TW Hydrae, as well as the Taurus-Auriga
association. We show that for appropriately chosen stars, JWST/NIRISS operating
in the AMI mode can image sub-Jupiter companions near the water frost-lines
with ~68% confidence. Among these, M-type stars are the most promising. We also
show that this JWST mode will improve the minimum inner working angle by as
much as ~50% in most cases when compared to the survey results from the best
ground-based exoplanet direct imaging facilities (e.g. VLT/SPHERE). We also
discuss how the NIRISS/AMI mode will be especially powerful for the
mid-infrared characterization of the numerous exoplanets expected to be
revealed by Gaia. When combined with dynamical masses from Gaia, such
measurements will provide a much more robust characterization of the initial
entropies of these young planets, thereby placing powerful constraints on their
early thermal histories.
