  Alpha Centauri A is the closest solar-type star to the Sun and offers an
excellent opportunity to detect the thermal emission of a mature planet heated
by its host star. The MIRI coronagraph on JWST can search the 1-3 AU (1"-2")
region around alpha Cen A which is predicted to be stable within the alpha Cen
AB system. We demonstrate that with reasonable performance of the telescope and
instrument, a 20 hr program combining on-target and reference star observations
at 15.5 um could detect thermal emission from planets as small as ~5 RE.
Multiple visits every 3-6 months would increase the geometrical completeness,
provide astrometric confirmation of detected sources, and push the radius limit
down to ~3 RE. An exozodiacal cloud only a few times brighter than our own
should also be detectable, although a sufficiently bright cloud might obscure
any planet present in the system. While current precision radial velocity (PRV)
observations set a limit of 50-100 ME at 1-3 AU for planets orbiting alpha Cen
A, there is a broad range of exoplanet radii up to 10 RE consistent with these
mass limits. A carefully planned observing sequence along with state-of-the-art
post-processing analysis could reject the light from alpha Cen A at the level
of ~10^-5 at 1"-2" and minimize the influence of alpha Cen B located 7-8" away
in the 2022-2023 timeframe. These space-based observations would complement
on-going imaging experiments at shorter wavelengths as well as PRV and
astrometric experiments to detect planets dynamically. Planetary demographics
suggest that the likelihood of directly imaging a planet whose mass and orbit
are consistent with present PRV limits is small, ~5%, and possibly lower if the
presence of a binary companion further reduces occurrence rates. However, at a
distance of just 1.34 pc, alpha Cen A is our closest sibling star and certainly
merits close scrutiny.
