Venus’ Bulk and Mantle Compositions: Are Venus and Earth Really Twins?

Introduction: Venus is Earth’s twin in size and bulk density [1], but obviously has a very different climate and climate history. Direct comparison of their histories [2] assumes implicitly that they have similar chemical compositions and internal structures; parts of these assumptions are testable with Venera and VEGA chemical analyses of Venus’ surface. From available chemical analyses, it is reasonable that the Earth and Venus are indeed twins, with similar bulk compositions (at least for non-atmophile elements), mantle compositions, and core sizes [3,4]. Such similarity between Earth and Venus is not necessarily consistent with current models of planetary accretion. Principles: Solar system planetary bodies apparently all accreted with cosmochemically refractory elements (e.g., U, Th, Ca, Ti, Al, Mg) in nearly the