  In this work, we investigate the thermophysical properties of OSIRIS-REx
target asteroid (101955) Bennu (hereafter, Bennu), where thermal inertia plays
an important role in understanding the nature of the asteroid's surface, and
will definitely provide substantial information for the sampling return
mission. Using a thermophysical model incorporating the recently updated 3D
radar-derived shape model \citep{Nolan2013} and mid-infrared observations of
Spitzer-PUI, Spitzer-IRAC, Herschel/PACS and ESO VLT/VISIR
\citep{Muller2012,Emery2014}, we derive the surface thermophysical properties
of Bennu. The asteroid has an effective diameter of $510^{+6}_{-40}$ m, a
geometry 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 a best-fit solution at
1$\sigma$ level. The best-estimate thermal inertia indicates that fine-grained
regolith may cover a large area of Bennu's surface, with a grain size that may
range from $1.3$ to $31$~mm, and our outcome further supports that Bennu would
be a suitable target for the OSIRIS-REx mission to return samples from the
asteroid to Earth.
