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The Missing Channels: N-body Population Synthesis of Free-Floating Planet Ejection Pathways for Roman GBTDS Interpretation
Program ID 19040
Science Category Exoplanets & Exoplanet Formation
Program Type Analysis
Category Medium
Principal Investigator Jeremy Smallwood
PI Institution Baylor University
Co-Investigators
  • Matthew De Furio (University of Texas, Austin)
  • William DeRocco (University of Maryland, College Park)
Abstract Free-floating planetary-mass objects (FFPMOs) may outnumber stars in the Milky Way, yet the mechanisms responsible for their production remain poorly constrained. The Roman Space Telescope's Galactic Bulge Time Domain Survey (GBTDS) will detect thousands of FFPMO microlensing events with sensitivity down to Earth-mass scales, necessitating a comprehensive theoretical framework to interpret these observations. The current state-of-the-art Galactic FFPMO mass distribution omits three dynamically vital ejection channels: (1) S-type ejections from misaligned binaries, where von Zeipel–Kozai–Lidov oscillations in the dominant ~50 au separation population drive rapid planetary unbinding; (2) ejections from hierarchical triple star systems, where tertiary-driven secular oscillations provide an efficient pathway operating on timescales orders of magnitude shorter than binary secular evolution; and (3) cumulative cluster encounters, where repeated sub-critical stellar flybys progressively destabilize planetary orbits over tens of millions of years. We propose a theoretical investigation to quantify these three missing channels through comprehensive N-body parameter surveys using REBOUND, weighted by observed Galactic stellar demographics. We will integrate our results with existing predictions for single-star, circumbinary, and ultra-wide binary systems to construct the first complete, multi-channel Galactic FFPMO mass distribution. Finally, we will embed this unified model within a Hierarchical Bayesian framework that forward models ejection mass-velocity distributions into Roman microlensing observables, thereby enabling direct constraints on the fractional contribution of each ejection channel from GBTDS event catalogs. This work will provide the theoretical foundation necessary to unlock the full diagnostic power of Roman's FFPMO detections.