  The collision of the NASA DART spacecraft with asteroid Dimorphos resulted in
the formation of a distinctive and long-lived debris trail, formed by the
action of solar radiation pressure on ejected particles. This trail briefly
displayed a double appearance, which has been interpreted as the result of a
double ejection. We present a model which can produce a transient double trail
without the need to assume a double ejection. Our model explains the appearance
of the double trail as a projection of the cone walls when viewed from a large
angle to the cone axis and avoids the problem of producing dust in two epochs
from a single, instantaneous impact. The particles follow a broken power-law
size distribution, with differential indices q = 2.7+/-0.2 (1 um <= a <= 2 mm),
3.9+/-0.1 (2 mm < a <= 1 cm), and 4.2+/-0.2 (1 cm < a <= 20 cm). We find that
the total trail mass in particles from 1 um to 20 cm in size (for an assumed
density 3500 kg/m3) is ~1.7e7 kg, rising to 2.2e7 kg, when extended to boulders
up to 3.5 m in radius. This corresponds to 0.4-0.6% of the mass of Dimorphos.
