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Geodetic analysis of radio tracking measurements of the MErcury Surface, Space ENvironment, GEochemistry, and Ranging spacecraft while in orbit about Mercury has yielded new estimates for the planet's gravity field, tidal Love number, and pole coordinates. The derived right ascension (alpha =281.0082 degrees +/- 0.0009 degrees; all uncertainties are 3 standard deviations) and declination (delta = 61.4164 degrees +/- 0.0003 degrees) of the spin pole place Mercury in the Cassini state. Confirmation of the equilibrium state with an estimated mean (whole planet) obliquity epsilon of 1.968 +/- 0.027 arcmin enables the confident determination of the planet's normalized polar moment of inertia (0.333 +/- 0.005), which indicates a high degree of internal differentiation. Internal structure models generated by a Markov Chain Monte Carlo process and consistent with the geodetic constraints possess a solid inner core with a radius (r(ic)) between 0.3 and 0.7 that of the outer core (r(oc)).