  The Gemini Planet Imager (GPI) is a high performance adaptive optics system
being designed and built for the Gemini Observatory. GPI is optimized for high
contrast imaging, combining precise and accurate wavefront control, diffraction
suppression, and a speckle-suppressing science camera with integral field and
polarimetry capabilities. The primary science goal for GPI is the direct
detection and characterization of young, Jovian-mass exoplanets. For plausible
assumptions about the distribution of gas giant properties at large semi-major
axes, GPI will be capable of detecting more than 10% of gas giants more massive
than 0.5 M_J around stars younger than 100 Myr and nearer than 75 parsecs. For
systems younger than 1 Gyr, gas giants more massive than 8 M_J and with
semi-major axes greater than 15 AU are detected with completeness greater than
50%. A survey targeting young stars in the solar neighborhood will help
determine the formation mechanism of gas giant planets by studying them at ages
where planet brightness depends upon formation mechanism. Such a survey will
also be sensitive to planets at semi-major axes comparable to the gas giants in
our own solar system. In the simple, and idealized, situation in which planets
formed by either the "hot-start" model of Burrows et al. (2003) or the core
accretion model of Marley et al. (2007), a few tens of detected planets are
sufficient to distinguish how planets form.
