  We explore the effects of collisional evolution on putative Vulcanoid
ensembles in the region between 0.06 and 0.21 AU from the Sun, in order to
constrain the probable population density and population structure of this
region today. Dynamical studies have shown that the Vulcanoid Zone (VZ) could
be populated. However, we find that the frequency and energetics of collisional
evolution this close to the Sun, coupled with the efficient radiation transport
of small debris out of this region, together conspire to create an active and
highly intensive collisional environment which depletes any very significant
population of rocky bodies placed in it, unless the bodies exhibit orbits that
are circular to ~10^-3 or less, or highly lossy mechanical properties that
correspond to a fraction of impact energy significantly less than 10% being
imparted to ejecta. The most favorable locale for residual bodies to survive in
this region is in highly circular orbits near the outer edge of the dynamically
stable Vulcanoid Zone (i.e., near 0.2 AU), where collisional evolution and
radiation transport of small bodies and debris proceed most slowly. If the mean
random orbital eccentricity in this region exceeds ~10^-3, then our work
suggests it is unlikely that more than a few hundred objects with radii larger
than 1 km will be found in the entire VZ; assuming the largest objects have a
radius of 30 km, then the total mass of bodies in the VZ down to 0.1 km radii
is likely to be no more than ~10^-6Mearth, <10^-3 the mass of the asteroid
belt. Despite the dynamical stability of large objects in this region (Evans &
Tabachnik 1999), it is plausible that the entire region is virtually empty of
km-scale and larger objects.
