Super-earths and mini-neptunes follow different orbital period-eccentricity relations

Abstract

Many exoplanets have been observed with radius sizes between that of Earth and that of Neptune and are thus classified into two groups: super-earths (SEs) and mini-neptunes (MNs). There are no SEs and MNs in the Solar System, and the mechanisms responsible for their formation and evolution are debated. We investigate the relationships between the orbital period and eccentricity of SEs and MNs using both ensemble analyses and individual measurements. We found that MNs follow an anti-correlation between orbital period and eccentricity, but SEs follow a different relation, possibly in the opposite direction. These trends imply that MNs and SEs are dynamically distinct populations. We suggest that SEs have been more strongly influenced by violent processes such as gravitational scattering and giant impacts, whereas MNs predominantly experienced quiescent secular evolution.

arXiv commentThis is the author's version of the work. It is posted here by permission of the AAAS for personal use, not for redistribution. The definitive version was published in Science on June 11th, 2026

References in corpus (60)

• Gaia Data Release 2. Summary of the contents and survey properties
• The Gaia mission
• Gaia Data Release 3: Summary of the content and survey properties
• The California-Kepler Survey. III. A Gap in the Radius Distribution of Small Planets
• Planet Occurrence within 0.25 AU of Solar-type Stars from Kepler
• Characteristics of planetary candidates observed by Kepler, II: Analysis of the first four months of data
• Dynamical Outcomes of Planet-Planet Scattering
• The NASA Exoplanet Archive: Data and Tools for Exoplanet Research
• Architecture of Kepler's Multi-transiting Systems: II. New investigations with twice as many candidates
• Origins of Hot Jupiters
• Growth Model Interpretation of Planet Size Distribution
• An asteroseismic view of the radius valley: stripped cores, not born rocky
• Origins of Eccentric Extrasolar Planets: Testing the Planet-Planet Scattering Model
• The Minimum-Mass Extrasolar Nebula: In-Situ Formation of Close-In Super-Earths
• Secular Chaos and the Production of Hot Jupiters
• Planetary Candidates Observed by Kepler. VIII. A Fully Automated Catalog With Measured Completeness and Reliability Based on Data Release 25
• Tidal Evolution of Close-in Extra-Solar Planets
• Eccentricity Evolution for Planets in Gaseous Disks
• Dearth of short-period Neptunian exoplanets - a desert in period-mass and period-radius planes
• Revised Radii of Kepler Stars and Planets Using Gaia Data Release 2
• Eccentricity from transit photometry: small planets in Kepler multi-planet systems have low eccentricities
• Density, not radius, separates rocky and water-rich small planets orbiting M dwarf stars
• About 30% of Sun-like Stars Have Kepler-like Planetary Systems: A Study of their Intrinsic Architecture
• The orbital eccentricity of small planet systems
• A Plateau in the Planet Population Below Twice the Size of Earth
• Revisited Mass-Radius relations for exoplanets below 120 Earth masses
• Exoplanet Orbital Eccentricities Derived From LAMOST-Kepler Analysis
• Giant planets orbiting metal-rich stars show signatures of planet-planet interactions
• A short-period censor of sub-Jupiter mass exoplanets with low density
• Atmospheric Mass Loss During Planet Formation: The Importance of Planetesimal Impacts
• The Gaia-Kepler Stellar Properties Catalog. II. Planet Radius Demographics as a Function of Stellar Mass and Age
• The statistics of multi-planet systems
• Tidal dissipation compared to seismic dissipation: in small bodies, in earths, and in superearths
• Habitable Climates: The Influence of Eccentricity
• Forward and Inverse Modeling of the Emission and Transmission Spectrum of GJ 436b: Investigating Metal Enrichment, Tidal Heating, and Clouds
• AMD-stability and the classification of planetary systems
• On The Relative Sizes of Planets Within Kepler Multiple Candidate Systems
• Characterizing the Orbital Eccentricities of Transiting Extrasolar Planets with Photometric Observations
• Quantification of tidal parameters from Solar system data
• Correlations between compositions and orbits established by the giant impact era of planet formation
• Giant Impact: An Efficient Mechanism for the Devolatilization of Super-Earths
• Orbital and physical properties of planets and their hosts: new insights on planet formation and evolution
• A Super-Solar Metallicity For Stars With Hot Rocky Exoplanets
• Habitability of planets on eccentric orbits: the limits of the mean flux approximation
• The Exoplanet Orbital Eccentricity - Multiplicity Relation and the Solar System
• Occurrence and Architecture of Kepler Planetary Systems as Functions of Stellar Mass and Effective Temperature
• Statistical properties of exoplanets IV. The period--eccentricity relations of exoplanets and of binary stars
• Planetary Collisions outside the Solar System: Time Domain Characterization of Extreme Debris Disks
• CKS VIII: Eccentricities of Kepler Planets and Tentative Evidence of a High Metallicity Preference for Small Eccentric Planets
• The Kepler Dichotomy in Planetary Disks: Linking Kepler Observables to Simulations of Late-Stage Planet Formation
• A Minimum-Mass Extrasolar Nebula
• Why do warm Neptunes present nonzero eccentricity?
• Observational biases for transiting planets
• Mapping the exo-Neptunian landscape. A ridge between the desert and savanna
• A Mechanism of Exciting Planetary Inclination and Eccentricity through a Residual Gas Disk
• Formation of Close-in Super-Earths by Giant Impacts: Effects of Initial Eccentricities and Inclinations of Protoplanets
• CKS IX: Revisiting the Minimum-Mass Extrasolar Nebula with Precise Stellar Parameters
• Proximity of exoplanets to first-order mean-motion resonances
• Chaotic Excitation and Tidal Damping in the GJ 876 System
• Planetary Orbit Eccentricity Trends (POET). I. The Eccentricity-Metallicity Trend for Small Planets Revealed by the LAMOST-Gaia-Kepler Sample