From super-Earths to sub-Neptunes: Observational constraints and connections to theoretical models

Abstract

We have updated the PlanetS catalog of transiting planets with precise and robust mass and radius measurements and use this catalog to explore mass-radius (M-R) diagrams. On the one hand, we propose new M-R relationships to separate exoplanets into three populations. On the other hand, we explore the transition in radius and density between super-Earths and sub-Neptunes around M-dwarfs and compare them with those orbiting K- and FG-dwarfs. Using Kernel density estimation method with a re-sampling technique, we estimated the normalized density and radius distributions, revealing connections between observations and theories on composition, internal structure, formation, and evolution of these exoplanets orbiting different spectral types. The 30% increase in the number of well-characterized exoplanets orbiting M-dwarfs compared with previous studies shows us that there is no clear gap in either composition or radius between super-Earths and sub-Neptunes. The "water-worlds" around M-dwarfs cannot correspond to a distinct population, their bulk density and equilibrium temperature can be interpreted by several different internal structures and compositions. The continuity in the fraction of volatiles in these planets suggests a formation scenario involving planetesimal or hybrid pebble-planetesimal accretion. We find that the transition between super-Earths and sub-Neptunes appears to happen at different masses (and radii) depending on the spectral type of the star. The maximum mass of super-Earths seems to be close to 10~M${}_{\oplus }$ for all spectral types, but the minimum mass of sub-Neptunes increases with the star's mass. This effect, attributed to planet migration, also contributes to the fading of the radius valley for M-planets compared to FGK-planets. While sub-Neptunes are less common around M-dwarfs, smaller ones exhibit lower density than their equivalents around FGK-dwarfs.

arXiv comment18 pages, 11 figures. Accepted for publication in A&A, version with language corrections. (Full abstract in the article)

References in corpus (84)

• The Gaia mission
• Gaia Data Release 3: Summary of the content and survey properties
• The Transiting Exoplanet Survey Satellite
• Intrinsic Colors, Temperatures, and Bolometric Corrections of Pre-Main Sequence Stars
• The K2 Mission: Characterization and Early results
• The California-Kepler Survey. III. A Gap in the Radius Distribution of Small Planets
• The PLATO 2.0 Mission
• Most 1.6 Earth-Radius Planets are not Rocky
• The evaporation valley in the Kepler planets
• Understanding the Mass-Radius Relation for Sub-Neptunes: Radius as a Proxy for Composition
• Detection of oxygen and carbon in the hydrodynamically escaping atmosphere of the extrasolar planet HD209458b
• The HARPS search for southern extra-solar planets XXXI. The M-dwarf sample
• The Occurrence Rate of Small Planets around Small Stars
• Probabilistic Forecasting of the Masses and Radii of Other Worlds
• A Framework for Prioritizing the TESS Planetary Candidates Most Amenable to Atmospheric Characterization
• The Mass-Radius Relation for 65 Exoplanets Smaller than 4 Earth Radii
• Growth Model Interpretation of Planet Size Distribution
• Extreme Water Loss and Abiotic O${}_2$ Buildup On Planets Throughout the Habitable Zones of M Dwarfs
• Homogeneous studies of transiting extrasolar planets. IV. Thirty systems with space-based light curves
• KEPLER's First Rocky Planet: Kepler-10b
• The California Kepler Survey VII. Precise Planet Radii Leveraging Gaia DR2 Reveal the Stellar Mass Dependence of the Planet Radius Gap
• An asteroseismic view of the radius valley: stripped cores, not born rocky
• Core-powered mass loss and the radius distribution of small exoplanets
• The James Webb Space Telescope Mission
• A torque formula for non-isothermal Type I planetary migration - I. Unsaturated horseshoe drag
• Mass-Radius Relation for Rocky Planets based on PREM
• Sculpting the Valley in the Radius Distribution of Small Exoplanets as a by-product of Planet Formation: The Core-Powered Mass-Loss Mechanism
• A New Family of Planets ? "Ocean Planets"
• Extracting Planet Mass and Eccentricity From TTV data
• A stellar-mass-dependent drop in planet occurrence rates
• The Mass of KOI-94d and a Relation for Planet Radius, Mass, and Incident Flux
• Density, not radius, separates rocky and water-rich small planets orbiting M dwarf stars
• Compositional imprints in density-distance-time: a rocky composition for close-in low-mass exoplanets from the location of the valley of evaporation
• Revisited Mass-Radius relations for exoplanets below 120 Earth masses
• The habitability of Proxima Centauri b. I. Irradiation, rotation and volatile inventory from formation to the present
• Kepler Planet Masses and Eccentricities from TTV Analysis
• The New Generation Planetary Population Synthesis (NGPPS). IV. Planetary systems around low-mass stars
• Bayesian Analysis of Hot Jupiter Radius Anomalies: Evidence for Ohmic Dissipation?
• They are Small Worlds After All: Revised Properties of Kepler M Dwarf Stars and their Planets
• The Gaia-Kepler Stellar Properties Catalog. II. Planet Radius Demographics as a Function of Stellar Mass and Age
• Evolution of the radius valley around low mass stars from $Kepler$ and $K2$
• HAZMAT I: The Evolution of Far-UV and Near-UV Emission from Early M Stars
• The Solar Neighborhood XXXV: Distances to 1404 M Dwarf Systems Within 25 pc in the Southern Sky
• Evolution of Ohmically Heated Hot Jupiters
• The New Generation Planetary Population Synthesis (NGPPS). II. Planetary population of solar-like stars and overview of statistical results
• Irradiated ocean planets bridge super-Earth and sub-Neptune populations
• Mass-radius relationships for irradiated ocean planets
• A Definition for Giant Planets Based on the Mass-Density Relationship
• The formation of Jupiter by hybrid pebble-planetesimal accretion
• Warm terrestrial planet with half the mass of Venus transiting a nearby star
• Revised mass-radius relationships for water-rich rocky planets more irradiated than the runaway greenhouse limit
• Conclusive evidence for a population of water-worlds around M-dwarfs remains elusive
• Two Empirical Regimes of the Planetary Mass-Radius Relation
• Superabundance of Exoplanet Sub-Neptunes Explained by Fugacity Crisis
• Formation and composition of planets around very low mass stars
• Habitability of planets on eccentric orbits: the limits of the mean flux approximation
• The CARMENES search for exoplanets around M dwarfs. Two planets on the opposite sides of the radius gap transiting the nearby M dwarf LTT 3780
• The Habitable-zone Planet Finder Reveals A High Mass and a Low Obliquity for the Young Neptune K2-25b
• Investigating hot-Jupiter inflated radii with hierarchical Bayesian modelling
• A deep radius valley revealed by Kepler short cadence observations
• The Equilibrium Temperature of Planets in Elliptical Orbits
• The Occurrence Rate of Terrestrial Planets Orbiting Nearby Mid-to-late M Dwarfs from TESS Sectors 1-42
• Creating the Radius Gap without Mass Loss
• A More Precise Mass for GJ 1214 b and the Frequency of Multi-Planet Systems Around Mid-M Dwarfs
• GJ 367b is a dark, hot, airless sub-Earth
• Giant planet formation at the pressure maxima of protoplanetary disks II. A hybrid accretion scenario
• A fading radius valley towards M-dwarfs, a persistent density valley across stellar types
• Mass-Radius relationship for M dwarf exoplanets: Comparing nonparametric and parametric methods
• The mass-radius relation of exoplanets, revisited
• HAZMAT VI: The Evolution of Extreme Ultraviolet Radiation Emitted from Early M Star
• Pebbles versus planetesimals: the outcomes of population synthesis models
• The runaway greenhouse on subNeptune waterworlds
• The maximum mass of planetary embryos formed in core-accretion models
• Precise mass and radius of a transiting super-Earth planet orbiting the M dwarf TOI-1235: a planet in the radius gap?
• On the mass of gas giant planets: Is Saturn a failed gas giant?
• A cool runaway greenhouse without surface magma ocean
• Shallower radius valley around low-mass hosts: Evidence for icy planets, collisions or high-energy radiation scatter
• Company for the ultra-high density, ultra-short period sub-Earth GJ 367 b: discovery of two additional low-mass planets at 11.5 and 34 days
• Unbiasing the density of TTV-characterised sub-Neptunes: Update of the mass-radius relationship of 34 Kepler planets
• How does the mass and activity history of the host star affect the population of low-mass planets?
• TOI-1231 b: A Temperate, Neptune-Sized Planet Transiting the Nearby M3 Dwarf NLTT 24399
• Assessing $TESS$'s Yield of Rocky Planets Around Nearby M Dwarfs
• Transit Timing Variations in the three-planet system: TOI-270
• EDEN Survey: Small Transiting Planet Detection Limits and Constraints on the Occurrence Rates for Late M Dwarfs within 15 pc

Cited by in corpus (45)

• JWST/NIRISS reveals the water-rich "steam world" atmosphere of GJ 9827 d
• TOI-5005 b: A super-Neptune in the savanna near the ridge
• NIRPS joining HARPS at ESO 3.6 m. On-sky performance and science objectives
• Convective shutdown in the atmospheres of lava worlds
• Giant exoplanet composition: Why do the hydrogen-helium equation of state and interior structure matter?
• Constraining exoplanet interiors using observations of their atmospheres
• The bulk metallicity of giant planets around M stars
• Evolution of steam worlds: energetic aspects
• Unraveling the origin of giant exoplanets: Observational implications of convective mixing
• Characterisation of TOI-406 as showcase of the THIRSTEE program: A 2-planet system straddling the M-dwarf density gap
• Possible Evidence for the Presence of Volatiles on the Warm Super-Earth TOI-270 b
• Discovery of a cold giant planet and mass measurement of a hot super-Earth in the multi-planetary system WASP-132
• Can metal-rich worlds form by giant impacts?
• Searching for Hot Water World Candidates with CHEOPS: Refining the radii and analysing the internal structures and atmospheric lifetimes of TOI-238 b and TOI-1685 b
• Volatile-rich evolution of molten super-Earth L 98-59 d
• Not All Sub-Neptune Exoplanets Have Magma Oceans
• NIRPS and TESS reveal a peculiar system around the M dwarf TOI-756: A transiting sub-Neptune and a cold eccentric giant
• TOI-3288 b and TOI-4666 b: two gas giants transiting low-mass stars characterised by NIRPS
• Tidally Heated Sub-Neptunes, Refined Planetary Compositions, and Confirmation of a Third Planet in the TOI-1266 System
• Earth-like planets hosting systems: Architecture and properties
• Radius valley scaling among low mass stars with TESS
• TESS and HARPS-N unveil two planets transiting TOI-1453. A super-Earth and one of the lowest mass sub-Neptunes
• Super-Earth masses and stellar abundances from NIRPS reveal tentative evidence for water-rich formation around M dwarfs
• TOI-2322: two transiting rocky planets close to the stellar rotation period and its first harmonic
• Long-term evolution of the temperature structure in magnetized protoplanetary disks and its implication for the dichotomy of planetary composition
• How Internal Structure Shapes the Metallicity of Giant Exoplanets
• No Robust Statistical Evidence for a Population of Water Worlds in a 2025 Sample of Planets Orbiting M Stars
• Discovery of a Nearby Habitable Zone Super-Earth Candidate Amenable to Direct Imaging
• Earth-like planet predictor: A machine learning approach
• A transiting rocky super-Earth and a non-transiting sub-Neptune orbiting the M dwarf TOI-771
• Densities of small planets around the M dwarfs TOI-4336 A and TOI-4342 with ESPRESSO: Three sub-Neptunes, one super-Earth, and a Neptune-mass candidate
• Confirmation of the hot super-Neptune TOI-672 b with NIRPS and HARPS and Insights into the Neptunian desert around M dwarfs
• Evolution and Observable Properties of Rocky Planet Atmospheres
• A Validated Low-to-Intermediate Mass Planetary Interior Structure Model and New Mass-Radius Relations
• Impact of rotation on synthetic mass-radius relationships of two-layer rocky planets and water worlds
• Three Hot Jupiters transiting K-dwarfs with a significant heavy element mass
• Modelling the Milky Way's exoplanet population based on cosmological galaxy simulations
• Improved characterization of the TOI-2141 system: a dense sub-Neptune with non-transiting inner and outer companions
• NIRPS tightens the mass estimate of GJ 3090 b and detects a planet near the stellar rotation period
• Hidden Gems in TESS: sherlock finds two new rocky planets around nearby M dwarfs
• Multicolour Validation of Two Temperate Mini-Neptunes Around M-dwarf Habitable Zones
• Sibling Sub-Neptunes Around Sibling M Dwarfs: TOI-521 and TOI-912
• Discovery of a multi-planetary system orbiting the aged Sun-like star HD 224018
• A planet-host ratio relation to synthesize microlensing and transiting exoplanet demography from Roman
• Retention of primordial atmospheres through giant impacts