  Many asteroids are likely rubble-piles that are a collection of smaller
objects held together by gravity and possibly cohesion. These asteroids are
seismically shaken by impacts, which leads to excitation of their constituent
particles. As a result it has been suggested that their surfaces and
sub-surface interiors may be governed by a size sorting mechanism known as the
Brazil Nut Effect. We study the behavior of a model asteroid that is a
spherical, self-gravitating aggregate with a binary size-distribution of
particles under the action of applied seismic shaking. We find that above a
seismic threshold, larger particles rise to the surface when friction is
present, in agreement with previous studies that focussed on cylindrical and
rectangular box configurations. Unlike previous works we also find that size
sorting takes place even with zero friction, though the presence of friction
does aid the sorting process above the seismic threshold. Additionally we find
that while strong size sorting can take place near the surface, the innermost
regions remain unsorted under even the most vigorous shaking.
