Space missions have documented the chemical diversity and complexity of planets in our solar system. Astronomers have found thousands of exoplanets orbiting other stars in our galaxy. Almost every star in our galaxy has one or more orbiting planets and they appear to be much more diverse than the few sampled in our solar system. This diversity implies immense chemical, ceramic, geological, and mineralogical complexity. Constrained by the limited data, understanding this range of planets poses a classic inverse problem in materials science, namely, to constrain the composition, phase relations, and evolution of a planet based on a few remote observations of its properties. The purpose of this paper is to provide a general view of the Earth and of planets in our solar system and beyond, to introduce fundamental concepts of planetary structure and chemistry, and to identify outstanding questions and opportunities from the point of view of chemistry, materials science, and ceramics. This paper is composed of two parts. First, an introduction is followed by a discussion of the structure, geophysics, and phase equilibria in the Earth, to orient the non-geologic reader to the basic phenomena and concepts. This is followed by a loose transcription of a lecture given by Navrotsky at the (virtual) 2020 American Ceramic Society meeting. This talk stressed the evolving nature of planetary science, especially inspired by the discovery of myriads of exoplanets, highlighted the Materials of the Universe Center at Arizona State University, and briefly described and compared planets in our solar system. © 2021 The Authors. International Journal of Ceramic Engineering & Science published by Wiley Periodicals LLC. on behalf of the American Ceramic Society.
