Exoplanet Demographics
Understanding the frequency, sizes, orbits, and architectures of planetary systems is essential for constraining theories of planet formation and evolution, and for designing the next generation of exoplanet surveys. Our group develops statistical frameworks for measuring planet occurrence rates and characterizing planetary system architectures using Kepler, TESS, and ground-based survey data.
Key Projects
Occurrence Rates
We use Bayesian hierarchical models and Approximate Bayesian Computation (ABC) to measure how common planets are around FGK stars and M dwarfs, rigorously accounting for survey completeness, detection efficiency, and measurement uncertainties. We improved estimates of η⊕, the frequency of Earth-analogs in the habitable zones of Sun-like stars, by rigorously accounting for interaction of detection biases and measurement uncertainties. Current work includes the Searching for GEMS survey (Giant Exoplanets around M-dwarf Stars) to constrain the occurrence and bulk densities of giant planets around low-mass stars.
Planetary System Architectures (SysSim)
Our SysSim forward-modeling framework characterizes the distribution of planetay system *architectures*, that is features of planetary *systems* rather than individual planets (e.g., distributions of planet multiplicities, relative sizes, orbital spacing, and mutual inclinations. The latest version combines AMD-stable clustered architectures with photoevaporation-driven envelope mass loss, producing the first single multi-planet model to simultaneously reproduce the Kepler radius valley and the observed intra-system size similarity (the "peas-in-a-pod" pattern). SysSim also underpins "friends and foes" studies of how the presence of one planet conditions the occurrence of additional companions.
Mass-Radius Relationships
Connecting planet masses to radii requires probabilistic models that handle measurement uncertainties, upper limits, and dependence on additional variables such as stellar irradiation and host-star mass. Our work ranges from early probabilistic mass-radius relations for sub-Neptune-sized planets (Wolfgang, Rogers & Ford 2016) to the MRExo package, which uses non-parametric Bayesian methods to jointly model up to four observables simultaneously, revealing how bulk-composition trends evolve with insolation and stellar mass.
Selected Publications
- Searching for GEMS: The Occurrence of Giant Planets Orbiting M Dwarfs within 100 pc
Glusman, Rowen I. et al. (2026), AJ, 171, 146. abstract doi - Architectures of Exoplanetary Systems. IV: A Multi-planet Model for Reproducing the Radius Valley and Intra-system Size Similarity of Planets around Kepler's FGK Dwarfs
He, Matthias Y., Ford, Eric B. (2026), arXiv e-prints, arXiv:2601.13480. abstract doi - Discovery of a Nearby Habitable Zone Super-Earth Candidate Amenable to Direct Imaging
Beard, Corey et al. (2025), AJ, 170, 279. abstract doi - Are We There Yet? Challenges in Quantifying the Frequency of Earth Analogs in the Habitable Zone
Fernandes, Rachel B. et al. (2025), PASP, 137, 121001. abstract doi - Searching for GEMS: Confirmation of TOI-5573 b, a Cool, Saturn-like Planet Orbiting an M Dwarf
Fernandes, Rachel B. et al. (2025), AJ, 170, 55. abstract doi - Searching for Giant Exoplanets around M-dwarf Stars (GEMS) I: Survey Motivation
Kanodia, Shubham et al. (2024), AJ, 167, 161. abstract doi - Updated Catalog of Kepler Planet Candidates: Focus on Accuracy and Orbital Periods
Lissauer, Jack J. et al. (2024), \psj, 5, 152. abstract doi - Paths to robust exoplanet science yield margin for the Habitable Worlds Observatory
Stark, Christopher C. et al. (2024), Journal of Astronomical Telescopes, Instruments, and Systems, 10, 034006. abstract doi - Beyond Two-dimensional Mass─Radius Relationships: A Nonparametric and Probabilistic Framework for Characterizing Planetary Samples in Higher Dimensions
Kanodia, Shubham et al. (2023), ApJ, 956, 76. abstract doi - Debiasing the Minimum-mass Extrasolar Nebula: On the Diversity of Solid Disk Profiles
He, Matthias Y., Ford, Eric B. (2022), AJ, 164, 210. abstract doi - The Occurrence of Rocky Habitable-zone Planets around Solar-like Stars from Kepler Data
Bryson, Steve et al. (2021), AJ, 161, 36. abstract doi - Optimizing Radial Velocity Follow-up Strategies for Single-Transit Exoplanet Candidates
Gupta, Arvind F. et al. (2021), 113. abstract doi - Friends and Foes: Conditional Occurrence Rates of Exoplanet Companions and Their Impact on Radial Velocity Follow-up Surveys
He, Matthias Y., Ford, Eric B., Ragozzine, Darin (2021), AJ, 162, 216. abstract doi - Friends and Foes: The Conditional Occurrence of Planetary Companions to Transiting Exoplanets and their Impact on Radial Velocity Follow-up Observations
He, Matthias Y., Ford, Eric B., Ragozzine, Darin (2021), 122. abstract doi - Architectures of Exoplanetary Systems. II. An Increase in Inner Planetary System Occurrence toward Later Spectral Types for Kepler's FGK Dwarfs
He, Matthias Y., Ford, Eric B., Ragozzine, Darin (2021), AJ, 161, 16. abstract doi - Evidence for a Nondichotomous Solution to the Kepler Dichotomy: Mutual Inclinations of Kepler Planetary Systems from Transit Duration Variations
Millholland, Sarah C. et al. (2021), AJ, 162, 166. abstract doi - Architectures of Exoplanetary Systems. III. Eccentricity and Mutual Inclination Distributions of AMD-stable Planetary Systems
He, Matthias Y. et al. (2020), AJ, 160, 276. abstract doi - Sensitivity Analyses of Exoplanet Occurrence Rates from Kepler and Gaia
Shabram, Megan I. et al. (2020), AJ, 160, 16. abstract doi - Architectures of exoplanetary systems - I. A clustered forward model for exoplanetary systems around Kepler's FGK stars
He, Matthias Y., Ford, Eric B., Ragozzine, Darin (2019), MNRAS, 490, 4575-4605. abstract doi - Occurrence Rates of Planets Orbiting FGK Stars: Combining Kepler DR25, Gaia DR2, and Bayesian Inference
Hsu, Danley C. et al. (2019), AJ, 158, 109. abstract doi - Superabundance of Exoplanet Sub-Neptunes Explained by Fugacity Crisis
Kite, Edwin S. et al. (2019), ApJL, 887, L33. abstract doi - Improving the Accuracy of Planet Occurrence Rates from Kepler Using Approximate Bayesian Computation
Hsu, Danley C. et al. (2018), AJ, 155, 205. abstract doi - Evidence for Two Hot-Jupiter Formation Paths
Nelson, Benjamin E., Ford, Eric B., Rasio, Frederic A. (2017), AJ, 154, 106. abstract doi - Period Ratio Distribution of Near-Resonant Planets Indicates Planetesimal Scattering
Chatterjee, Sourav, Krantzler, Seth O., Ford, Eric B. (2016), IAU Focus Meeting, 29A, 30-37. abstract doi - Secure Mass Measurements from Transit Timing: 10 Kepler Exoplanets between 3 and 8 M_⊕ with Diverse Densities and Incident Fluxes
Jontof-Hutter, Daniel et al. (2016), ApJ, 820, 39. abstract doi - The Diversity of Low-mass Exoplanets Characterized via Transit Timing
Jontof-Hutter, Daniel et al. (2016), IAU Focus Meeting, 29A, 40-50. abstract doi - The Eccentricity Distribution of Short-period Planet Candidates Detected by Kepler in Occultation
Shabram, Megan et al. (2016), ApJ, 820, 93. abstract doi - The Small Exoplanet Mass-Radius Relation: Quantifying the Astrophysical Scatter
Wolfgang, Angie, Rogers, Leslie A., Ford, Eric B. (2016), IAU Focus Meeting, 29A, 223-223. abstract doi - Probabilistic Mass-Radius Relationship for Sub-Neptune-Sized Planets
Wolfgang, Angie, Rogers, Leslie A., Ford, Eric B. (2016), ApJ, 825, 19. abstract doi - Architecture of Kepler's Multi-transiting Systems. II. New Investigations with Twice as Many Candidates
Fabrycky, Daniel C. et al. (2014), ApJ, 790, 146. abstract doi - Planetary Candidates Observed by Kepler. III. Analysis of the First 16 Months of Data
Batalha, Natalie M. et al. (2013), ApJS, 204, 24. abstract doi - A Habitable Zone Census via Transit Timing and the Imperative for Continuing to Observe the Kepler Field
Fabrycky, Daniel C. et al. (2013), arXiv e-prints, arXiv:1309.1177. abstract doi - An abundance of small exoplanets around stars with a wide range of metallicities
Buchhave, Lars A. et al. (2012), Nature, 486, 375-377. abstract doi - Constraining the false positive rate for Kepler planet candidates with multicolour photometry from the GTC
Colón, Knicole D., Ford, Eric B., Morehead, Robert C. (2012), MNRAS, 426, 342-353. abstract doi - Transit Timing Observations from Kepler. V. Transit Timing Variation Candidates in the First Sixteen Months from Polynomial Models
Ford, Eric B. et al. (2012), ApJ, 756, 185. abstract doi - Planet Occurrence within 0.25 AU of Solar-type Stars from Kepler
Howard, Andrew W. et al. (2012), ApJS, 201, 15. abstract doi - Almost All of Kepler's Multiple-planet Candidates Are Planets
Lissauer, Jack J. et al. (2012), ApJ, 750, 112. abstract doi - Transiting circumbinary planets Kepler-34 b and Kepler-35 b
Welsh, William F. et al. (2012), Nature, 481, 475-479. abstract doi - The diverse origin of exoplanets' eccentricities \& inclinations
Ford, Eric B. (2011), 276, 221-224. abstract doi - Architecture and Dynamics of Kepler's Candidate Multiple Transiting Planet Systems
Lissauer, Jack J. et al. (2011), ApJS, 197, 8. abstract doi - The Distribution of Transit Durations for Kepler Planet Candidates and Implications for Their Orbital Eccentricities
Moorhead, Althea V. et al. (2011), ApJS, 197, 1. abstract doi - On the eccentricity distribution of short-period single-planet systems
Wang, Ji, Ford, Eric B. (2011), MNRAS, 418, 1822-1833. abstract doi - Observational biases in determining extrasolar planet eccentricities in single-planet systems
Zakamska, Nadia L., Pan, Margaret, Ford, Eric B. (2011), MNRAS, 410, 1895-1910. abstract doi - Kepler Planet-Detection Mission: Introduction and First Results
Borucki, William J. et al. (2010), Science, 327, 977. abstract doi - The Formation Mechanism of Gas Giants on Wide Orbits
Dodson-Robinson, Sarah E. et al. (2009), ApJ, 707, 79-88. abstract doi - Characterizing the Eccentricities of Transiting Extrasolar Planets with Kepler and CoRoT
Ford, Eric B., Colón, Knicole D. (2009), 253, 111-119. abstract doi - Formation, Survival, and Detectability of Planets Beyond 100 AU
Veras, Dimitri, Crepp, Justin R., Ford, Eric B. (2009), ApJ, 696, 1600-1611. abstract doi - Ten New and Updated Multiplanet Systems and a Survey of Exoplanetary Systems
Wright, J.~T. et al. (2009), ApJ, 693, 1084-1099. abstract doi - Characterizing the Orbital Eccentricities of Transiting Extrasolar Planets with Photometric Observations
Ford, Eric B., Quinn, Samuel N., Veras, Dimitri (2008), ApJ, 678, 1407-1418. abstract doi - Origins of Eccentric Extrasolar Planets: Testing the Planet-Planet Scattering Model
Ford, Eric B., Rasio, Frederic A. (2008), ApJ, 686, 621-636. abstract doi - Structure and Evolution of Nearby Stars with Planets. II. Physical Properties of ~1000 Cool Stars from the SPOCS Catalog
Takeda, Genya et al. (2007), ApJS, 168, 297-318. abstract doi - On the Relation between Hot Jupiters and the Roche Limit
Ford, Eric B., Rasio, Frederic A. (2006), ApJL, 638, L45-L48. abstract doi - On the relation between Hot-Jupiters and the Roche Limit
Ford, Eric B., Rasio, Frederic A. (2005), arXiv e-prints, astro-ph/0510198. abstract doi - Planet-Finding Prospects for the Space Interferometry Mission
Ford, Eric B., Tremaine, Scott (2003), PASP, 115, 1171-1186. abstract doi - Early-Type Stars: Most Favorable Targets for Astrometrically Detectable Planets in the Habitable Zone
Gould, Andrew, Ford, Eric B., Fischer, Debra A. (2003), ApJL, 591, L155-L158. abstract doi - Structure and Evolution of Nearby Stars with Planets. I. Short-Period Systems
Ford, Eric B., Rasio, Frederic A., Sills, Alison (1999), ApJ, 514, 411-429. abstract doi
Software
ExoplanetsSysSim.jl
Forward modeling framework for exoplanet demographics. Used to characterize the architectures of planetary systems from Kepler data.
SysSimExClusters
Draw samples of planetary systems consistent with Kepler observations.
Greatly Expedited Robust Box Least Squares (GRBLS)
lightweight fast-folding implementation of the BLS (Box Least Squares) algorithm
ApproximateBayesianComputing.jl
Algorithms for Approximate Bayesian Computing via Particle Monte Carlo (ABC-PMC).
MRExo
Nonparametric and probabilistic Python package for jointly modeling exoplanet mass-radius relationships and their dependence on additional observables (insolation, stellar mass). Supports asymmetric uncertainties and upper limits.