Presentation #400.02 in the session Formation and Demographics II.
Recent results on the characterization of small planets have presented two questions: (1) Is there a range of super-Earth and/or sub-Neptune formation mechanisms? and (2) What is the precise and accurate planet mass-radius relation in the < 3 REarth regime? The Magellan-TESS Survey (MTS) is designed to address these questions in a statistically robust and self-consistent framework, combining transiting and radial velocity techniques to connect observed planet distributions to true underlying populations and the processes that shape them. This talk will discuss the latest, end-of-survey results from the MTS, which includes mass constraints, host star compositions, and system architectures of 30 small planets detected by TESS across a range of insolation fluxes. Its statistical robustness arises from quantifiable and uniformly applied choices for transiting planet target selection and radial velocity observation cadencing. Its self-consistency arises from using the same observational tools (TESS, Magellan/PFS) and analysis across all targets. We will present our hierarchical Bayesian modeling of the empirical mass-radius relation, how it depends on insolation flux and system architecture (e.g., existence of outer gas giant), and insights from comparisons to the literature and physically-motivated interior models. Overall, the MTS-style approach to population studies will become increasingly important as we move deeper into the era of exoplanet characterization towards more habitable conditions, where observational constraints are more technically challenging and expensive.