  Asteroid (162173) Ryugu is the target object of Hayabusa2, an asteroid
exploration and sample return mission led by Japan Aerospace Exploration Agency
(JAXA). Ground-based observations indicate that Ryugu is a C-type near-Earth
asteroid with a diameter of less than 1 km, but the knowledge of its detailed
properties is still very limited. This paper summarizes our best understanding
of the physical and dynamical properties of Ryugu based on remote sensing and
theoretical modeling. This information is used to construct a design reference
model of the asteroid that is used for formulation of mission operations plans
in advance of asteroid arrival. Particular attention is given to the surface
properties of Ryugu that are relevant to sample acquisition. This reference
model helps readers to appropriately interpret the data that will be directly
obtained by Hayabusa2 and promotes scientific studies not only for Ryugu itself
and other small bodies but also for the Solar System evolution that small
bodies shed light on.
