  In this work, we investigate the thermophysical properties, including thermal
inertia, roughness fraction and surface grain size of OSIRIS-REx target
asteroid (101955) Bennu by using a thermophysical model with the recently
updated 3D radar-derived shape model (\cite[Nolan et al., 2013]{Nolan2013}) and
mid-infrared observations (\cite[M$\ddot{u}$ller et al, 2012]{Muller2012},
\cite[Emery et al., 2014]{Emery2014}). We find that the asteroid bears an
effective diameter of $510^{+6}_{-40}$ m, a geometric albedo of
$0.047^{+0.0083}_{-0.0011}$, a roughness fraction of $0.04^{+0.26}_{-0.04}$,
and thermal inertia of $240^{+440}_{-60}\rm~Jm^{-2}s^{-0.5}K^{-1}$ for our
best-fit solution. The best-estimate thermal inertia suggests that fine-grained
regolith may cover a large portion of Bennu's surface, where a grain size may
vary from $1.3$ to $31$~mm. Our outcome suggests that Bennu is suitable for the
OSIRIS-REx mission to return samples to Earth.
