  We describe the expected scientific capabilities of CHARIS, a high-contrast
integral-field spectrograph (IFS) currently under construction for the Subaru
telescope. CHARIS is part of a new generation of instruments, enabled by
extreme adaptive optics (AO) systems (including SCExAO at Subaru), that promise
greatly improved contrasts at small angular separation thanks to their ability
to use spectral information to distinguish planets from quasistatic speckles in
the stellar point-spread function (PSF). CHARIS is similar in concept to GPI
and SPHERE, on Gemini South and the Very Large Telescope, respectively, but
will be unique in its ability to simultaneously cover the entire near-infrared
$J$, $H$, and $K$ bands with a low-resolution mode. This extraordinarily broad
wavelength coverage will enable spectral differential imaging down to angular
separations of a few $\lambda/D$, corresponding to $\sim$$0.\!\!''1$. SCExAO
will also offer contrast approaching $10^{-5}$ at similar separations,
$\sim$$0.\!\!''1$--$0.\!\!''2$. The discovery yield of a CHARIS survey will
depend on the exoplanet distribution function at around 10 AU. If the
distribution of planets discovered by radial velocity surveys extends unchanged
to $\sim$20 AU, observations of $\sim$200 mostly young, nearby stars targeted
by existing high-contrast instruments might find $\sim$1--3 planets. Carefully
optimizing the target sample could improve this yield by a factor of a few,
while an upturn in frequency at a few AU could also increase the number of
detections. CHARIS, with a higher spectral resolution mode of $R \sim 75$, will
also be among the best instruments to characterize planets and brown dwarfs
like HR 8799 cde and $\kappa$ And b.
