The densities and bulk compositions of Ceres and Vesta

Present radiometric and polarimetric measurements of the sizes and albedos of asteroids 1 Ceres and 4 Vesta, although uncertain in absolute calibration, determine the ratio of diameters with sufficient precision (Ceres/Vesta = 1.87 ± 0.03) to permit meaningful discussion of their relative densities. These measurements combined with the known masses yield a ratio of densities Vesta/Ceres = 1.33 ± 0.17, thus demonstrating that: (1) the bulk compositions are likely different, and (2) the difference is consistent with indications from remotely‐determined surface composition that Vesta is differentiated while Ceres may be of undifferentiated carbonaceous chondritic composition.