  Objects in the Edgeworth-Kuiper belt and the main asteroid belt should emit
microwaves that may give rise to extra anisotropy signals in the multipole of
the cosmic microwave background (CMB) experiment. Constraints are derived from
the absence of positive detection of such anisotropies for ell < 50, giving the
total mass of Edgeworth-Kuiper belt objects to be smaller than 0.2 earth mass.
This limit is consistent with the mass extrapolated from the observable
population with the size of a > 15 km, assuming that the small-object
population follows the power law in size dN/da ~ a^{-q} with the canonical
index expected for collisional equilibrium, q ~ 3.5, with which 23% of the mass
is ascribed to objects smaller than are observationally accessible down to
grains. A similar argument applied to the main asteroid belt indicates that the
grain population should not increase faster than q ~ 3.6 towards smaller radii,
if it follows the power law continued to observed asteroids with larger radii.
It is underlined that both cases are at or only slightly above the limit that
can be physically significant, implying the importance of tightening further
the CMB anisotropy limit, which may be attained with the observation at higher
radio frequencies.
