Completing the Census of Exoplanets with the Microlensing Planet Finder
  (MPF)
  The MPF mission will provide a statistical census of exoplanets with masses
greater than 0.1 Earth-masses and orbital separations ranging from 0.5AU to
infinity. This includes analogs to all the Solar System's planets except for
Mercury, as well as most types of planets predicted by planet formation
theories. Such a survey will provide results on the frequency of planets around
all types of stars except those with short lifetimes. Close-in planets with
separations < 0.5 AU are invisible to a space-based microlensing survey, but
these can be found by Kepler. Other methods, including ground-based
microlensing, cannot approach the comprehensive statistics on the mass and
semi-major axis distribution of extrasolar planets that a space-based
microlensing survey will provide. The terrestrial planet sensitivity of a
ground-based microlensing survey is limited to the vicinity of the Einstein
radius at 2-3 AU, and space-based imaging is needed to identify and determine
the mass of the planetary host stars for the vast majority of planets
discovered by microlensing. Thus, a space-based microlensing survey is likely
to be the only way to gain a comprehensive understanding of the architecture of
planetary systems, which is needed to understand planet formation and
habitability. MPF can accomplish these objectives with proven technology and a
cost of $333 million (excluding launch vehicle).
