HARPS-N helps to determine the mass of Kepler-93b.
Implications on the composition of terrestrial planets.

86 radial velocity observations obtained with the HARPS-N on the Telescopio Nazionale Galileo (TNG), combined with the 32 archival Keck/HIRES measurements, allowed an international team of astronomers lead by Courtney Dressing of Harvard-Smithsonian Center for Astrophysics (CfA) to characterize Kepler-93b, an alien world only 1.5 times the radius of Earth. HARPS-N determined that Kepler-93b is just over 4 times Earth's mass, implying a rocky composition with a density of around 6.8 g/cc. This high density is consistent with a rocky composition of primarily iron and magnesium silicate. The team compared Kepler-93b to other dense planets with well-constrained parameters and found that between 1-6 Earth masses, all dense planets including the Earth and Venus are well-described by the same fixed ratio of iron to magnesium silicate. The astronomers are looking forward to test whether this compositional model will hold true while more dense planets with well-constrained densities will be discovered in the future.

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