  All known Small Solar System Bodies have diameters between a few meters and a
few thousands of kilometers. Based on the collisional evolution of Solar System
Bodies, a larger number of asteroids with diameters down to $\sim 2$ m is
thought to exist. As all Solar System Bodies, Small Bodies can be passive
sources of high-energy gamma rays, produced by the interaction of energetic
cosmic rays impinging on their surfaces. Since the majority of known asteroids
are in orbits between Mars and Jupiter (in a region known as the Main Belt), we
expect them to produce a diffuse emission close to the ecliptic plane. In this
work we have studied the gamma-ray emission coming from the ecliptic using the
data collected by the Large Area Telescope onboard the Fermi satellite. We have
fit the results with simulations of the gamma-ray intensity at source level
(calculated with the software FLUKA) to constrain the Small Solar System Bodies
population. Finally, we have proposed a model describing the distribution of
asteroid sizes and we have used the LAT data to constrain the gamma-ray
emission expected from this model and, in turn, on the model itself.
