  The rotational mass loss has been realized to be a prevalent mechanism to
produce low-speed debris near the asteroid, and the size composition of the
asteroid's surface regolith has been closely measured by in situ explorations.
However, the full-scale evolution of the shedding debris has not been examined
using the observed particle sizes, which may hold vital clues to the initial
growth of an asteroid moonlet, and help us to understand the general mechanisms
that dominate the formation of asteroid systems. This paper presented our study
on the cumulative evolution of the debris cloud formed by a rotationally
unstable asteroid. A semi-analytical model is developed to characterize the
spatial-temporal evolution of the debris cloud posterior to a shedding event.
Large-scale DEM simulations are performed to quantify the clustering behavior
of the debris particles in the mechanical environment near the asteroid. As a
result, we found the cumulation of a steady debris cloud is dominated by large
pieces of debris, and the shedding particles follow a common migration trend,
which fundamentally determines the mass distribution of the debris cloud. For
the accretion analysis, we sketched the life cycle of a debris cluster, and
showed its dependency on particle size. The DEM simulations adopt physical
parameters estimated from observations and asteroid missions. The results
confirm porous fluffy cluster structures can form shortly after a shedding
event of observed magnitude. Measurements to these structures show they possess
certain strength and adsorption capacity to collisions from dissociative debris
particles.
