UCLA

Polluted white dwarfs offer the rare chance to directly measure the bulk compositions of exoplanetary material. These stellar remnants are actively accreting exoplanetary debris, whose chemical abundances can be extrapolated from excess metal lines in white dwarf spectra. In this dissertation I leverage the growing sample of observed polluted white dwarfs to conduct statistical comparisons between exoplanetary rock compositions and objects in our solar system. My work combines data compiled from the literature along with analytical models for accretion and settling in white dwarf atmospheres to test the elemental abundances of white dwarf pollution, while placing constraints on how to best leverage white dwarf data given uncertainties in different accretion processes. I first validate exomoons as a potential source of white dwarf pollution, and show that the bulk objects causing pollution need to be massive, on the order of Vesta or Ceres, the largest objects in our asteroid belt. I then argue that the white dwarf sample is evidence that most nearby exoplanets form from compositional building blocks similar to CI chondrites, the assumed primitive material in our own solar system. I support this conclusion by showing that the relative abundances of rock-forming elements in nearby stars are similarly consistent with chondrites, and demonstrate that on very large scales, the chemical evolution of our galaxy may be encoded in planet compositions. Finally, I show that the oxygen abundances in polluted white dwarfs are consistent with water contents ranging from dry, Earth-like bodies to water-rich objects akin to icy moons in the solar system. These results place important constraints on the compositions of exoplanets, suggest that solar system compositions are not unique compared to our nearest neighbors, and provide the foundation for future studies on the formation and diversity of exoplanets in the Milky Way.