  The mass of CoRoT-7b, the first transiting superearth exoplanet, is still a
subject of debate. A wide range of masses have been reported in the literature
ranging from as high as 8 M_Earth to as low as 2.3 M_Earth. Although most mass
determinations give a density consistent with a rocky planet, the lower value
permits a bulk composition that can be up to 50% water. We present an analysis
of the CoRoT-7b radial velocity measurements that uses very few and simple
assumptions in treating the activity signal. By only analyzing those radial
velocity data for which multiple measurements were made in a given night we
remove the activity related radial velocity contribution without any a priori
model. We demonstrate that the contribution of activity to the final radial
velocity curve is negligible and that the K-amplitude due to the planet is well
constrained. This yields a mass of 7.42 +/- 1.21 M_Earth and a mean density of
rho = 10.4 +/- 1.8 gm cm^-3. CoRoT-7b is similar in mass and radius to the
second rocky planet to be discovered, Kepler-10b, and within the errors they
have identical bulk densities - they are virtual twins. These bulk densities
lie close to the density - radius relationship for terrestrial planets similar
to what is seen for Mercury. CoRoT-7b and Kepler-10b may have an internal
structure more like Mercury than the Earth.
