  We report the direct detection of radiation pressure on the asteroid 2009 BD,
one of the smallest multi-opposition near-Earth objects currently known, with H
~ 28.4. Under the purely gravitational model of NEODyS the object is currently
considered a possible future impactor, with impact solutions starting in 2071.
The detection of a radiation-related acceleration allows us to estimate an Area
to Mass Ratio (AMR) for the object, that can be converted (under some
assumptions) into a range of possible values for its average density. Our
result AMR = (2.97 \pm 0.33) x 10^(-4) m^2 kg^(-1) is compatible with the
object being of natural origin, and it is narrow enough to exclude a man-made
nature. The possible origin of this object, its future observability, and the
importance of radiation pressure in the impact monitoring process, are also
discussed.
