Kepler-93b is a 1.478 \pm 0.019 { R _ { \oplus } } planet with a 4.7 day period around a bright ( V = 10.2 ) , astroseismically-characterized host star with a mass of 0.911 \pm 0.033 { M _ { \odot } } and a radius of 0.919 \pm 0.011 { R _ { \odot } } .
Based on 86 radial velocity observations obtained with the HARPS-N spectrograph on the Telescopio Nazionale Galileo and 32 archival Keck/HIRES observations , we present a precise mass estimate of 4.02 \pm 0.68 { M _ { \oplus } } .
The corresponding high density of 6.88 \pm 1.18 g/cc is consistent with a rocky composition of primarily iron and magnesium silicate .
We compare Kepler-93b to other dense planets with well-constrained parameters and find that between 1 - 6 { M _ { \oplus } } , all dense planets including the Earth and Venus are well-described by the same fixed ratio of iron to magnesium silicate .
There are as of yet no examples of such planets with masses > 6 { M _ { \oplus } } : All known planets in this mass regime have lower densities requiring significant fractions of volatiles or H/He gas .
We also constrain the mass and period of the outer companion in the Kepler-93 system from the long-term radial velocity trend and archival adaptive optics images .
As the sample of dense planets with well-constrained masses and radii continues to grow , we will be able to test whether the fixed compositional model found for the seven dense planets considered in this paper extends to the full population of 1 - 6 { M _ { \oplus } } planets .