  It has been pointed out that the Galactic satellites all have a common mass
around 1e7 Msun within 300 pc (M03), while they span almost four order of
magnitudes in luminosity (Mateo et al. 1993, Strigari et al. 2008). It is
argued that this may reflect a specific scale for galaxy formation or a scale
for dark matter clustering. Here we use numerical simulations coupled with a
semi-analytic model for galaxy formation, to predict the central mass and
luminosity of galactic satellites in the LCDM model. We show that this common
mass scale can be explained within the Cold Dark Matter scenario when the
physics of galaxy formation is taken into account. The narrow range of M03
comes from the narrow distribution of circular velocities at time of accretion
(peaking around 20 km/s) for satellites able to form stars and the not tight
correlation between halo concentration and circular velocity. The wide range of
satellite luminosities is due to a combination of the mass at time of accretion
and the broad distribution of accretion redshifts for a given mass. This causes
the satellites baryonic content to be suppressed by photo-ionization to very
different extents. Our results favor the argument that the common mass M03
reflects a specific scale (circular velocity ~ 20 km/s) for star formation.
