Orbital stability, high-eccentricity tidal migration, and the dynamical origins of hot Jupiters, warm Jupiters, sub-Saturns, and free-floating planets.
Dynamical and Secular Stability of Mutually Inclined Planetary Systems
Stability criteria for two-planet systems have mostly assumed near-coplanar orbits, leaving the role of mutual inclination poorly captured. This paper derives a semi-analytic stability criterion, valid at arbitrary mutual inclinations, from the perturbation-driven change in a test-particle inner orbit's semi-major axis. Among the findings: retrograde configurations are generally more stable than prograde ones, systems with intermediate mutual inclinations are the least stable due to Kozai–Lidov–type dynamics, and mean-motion resonances can either stabilize or destabilize particular regions of parameter space.
Properties of Free Floating Planets Ejected through Planet–Planet Scattering
Planet–planet scattering is a leading explanation for the growing observed population of free-floating (unbound) planets. Using a large suite of N-body simulations of multi-planet systems, this paper characterizes which planets get ejected, when, and how fast. Roughly 40–80% of planets are eventually ejected depending on how many planets a system starts with, with most ejections happening over 108–109 years and typical ejection speeds of a few km/s relative to the host star; matching the simulated population to observations suggests stars typically need to form 5–10 planets to reproduce the data.
Secularly-Driven High-Eccentricity Migration Predicts an Anti-Correlation between Period and Stellar Obliquity
An emerging observational trend is that the shortest-period hot Jupiters tend to be strongly misaligned with their star's spin, while longer-period hot Jupiters are usually well aligned. This paper shows that secular high-eccentricity migration driven by a distant planetary companion naturally reproduces this pattern: the shortest-period planets form through Kozai–Lidov–type excitation by highly inclined companions (producing a broad spread of obliquities), while the longest-period planets form more gradually through coplanar high-eccentricity migration that preserves low obliquities, with intermediate periods showing an intermediate spread.
Main-Sequence Systems: Orbital Stability around Single Star Hosts
A review chapter on the orbital stability of planetary systems around single stars, covering both compact multi-planet systems and hierarchical configurations. It surveys the main tools used to assess stability — direct N-body integration, semi-analytic stability criteria, and newer machine-learning approaches — as a reference for researchers and students working on exoplanetary system stability.
Thermally Regulated Viscoelastic Tidal Migration of Eccentric Planets
Many close-in, eccentric Neptune-like planets appear to be undergoing tidal circularization, but standard tidal models are built for gas giants rather than planets with rocky or icy cores. This paper models the coupled orbital and thermal evolution of an eccentric planet whose tides are dissipated in a viscoelastic core, and finds that the process is self-regulating: tidal heating raises the core temperature, which lowers viscosity and shifts the dissipation regime, slowing further migration. This feedback naturally produces long-lived eccentric phases and can explain why observed hot Neptunes retain eccentricity across a wide range of orbital distances.
High-Eccentricity Tidal Migration Driven by Secular Chaos in Wide-Binary Systems
Most models of high-eccentricity migration driven by a distant stellar companion use an idealized three-body setup, but real cold-Jupiter systems often carry additional planets or substellar companions. This paper studies hierarchical "3+1" systems—a stellar binary hosting a planet plus an intermediate companion—and shows that secular chaos, controlled by the ratio of the inner and outer Kozai–Lidov timescales, can drive migration even at fairly modest mutual inclinations, well below the classical Kozai–Lidov threshold. The model predicts resulting hot Jupiters on nearly polar orbits relative to both their host star and their outer companions.
Main-Sequence Systems: Orbital Stability in Stellar Binaries
A companion review chapter focused on planets in binary star systems, covering both planets orbiting one star of the pair (S-type) and planets orbiting both stars (P-type). It summarizes semi-analytic secular stability criteria alongside N-body and machine-learning results, aimed at researchers entering the study of circumbinary and S-type planet stability.
Additional co-authored exoplanet discovery and characterization papers.