The Compositional Diversity of Small Planets Orbiting Low-Mass Stars

Citation

Greklek-McKeon, Michael Christopher (2025) The Compositional Diversity of Small Planets Orbiting Low-Mass Stars. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/t2jp-m847. https://resolver.caltech.edu/CaltechTHESIS:06022025-194525159

Abstract

The Kepler and TESS missions have revealed that planets between the size of Earth and Neptune dominate our galaxy, showing a bimodal radius distribution that suggests distinct formation and evolution pathways. M dwarf stars offer the ideal opportunity to characterize these small planets due to their favorable planet-to-star size ratios. But M dwarf planets may differ fundamentally from those around Sun-like stars. Their cooler disk temperatures may result in more water-rich planet compositions, while their higher stellar activity rates may result in higher atmospheric mass loss rates. I investigate these questions by measuring planetary masses, radii, and bulk compositions with the first systematic transit timing variation survey of M dwarf planets discovered by the ongoing TESS survey, utilizing observations from Palomar Observatory and other small- to mid-sized telescopes. In this thesis, I present studies of four key systems from this survey: Kepler-289, where I improved planetary mass constraints by more than twofold and constrained the formation location of the outer gas giant companion; TOI-1266, where I characterized a potentially tidally heated planet with an inflated radius and a candidate water-world; LP 791-18, where I measured the bulk density of an Earth-sized planet and made predictions for its tidal heating rate that will be tested by upcoming JWST observations; and TOI-2267, a binary M dwarf system where I statistically validated a new Earth-sized planet with important implications for planet formation and migration. These systems have expanded our understanding of small planets around low-mass stars and provide valuable case studies for studies of atmospheric mass loss, the search for planets with water-rich envelopes, and the role of tidal heating in compact multi-planet systems.

Thesis Files