  Strange-looking dust cloud around asteroid (596) Scheila was discovered on
2010 December 11.44-11.47. Unlike normal cometary tails, it consisted of three
tails and faded within two months. We constructed a model to reproduce the
morphology of the dust cloud based on the laboratory measurement of high
velocity impacts and the dust dynamics. As the result, we succeeded in the
reproduction of peculiar dust cloud by an impact-driven ejecta plume consisting
of an impact cone and downrange plume. Assuming an impact angle of 45 deg, our
model suggests that a decameter-sized asteroid collided with (596) Scheila from
the direction of (alpha, delta) = (60deg, -40deg) in J2000 coordinates on 2010
December 3. The maximum ejection velocity of the dust particles exceeded 100
m/s. Our results suggest that the surface of (596) Scheila consists of
materials with low tensile strength.
