Super-Earths and Earth-like Exoplanets

Abstract

In the last few years astronomical surveys have expanded the reach of planetary science into the realm of small and dense extrasolar worlds. These share a number of characteristics with the terrestrial and icy planetary objects of the Solar System, but keep stretching previous understanding of the known limits of planetary thermodynamics, material properties, and climate regimes. Improved compositional and thermal constraints on exoplanets below $\sim$2 Earth radii suggest efficient accretion of atmosphere-forming volatile elements in a fraction of planetary systems, pointing to rapid formation, planet-scale melting, and chemical equilibration between the core, mantle, and atmosphere of rocky and volatile-rich exoplanets. Meaningful interpretation of novel observational data from these worlds necessitates cross-disciplinary expansion of known material properties under extreme thermodynamic, non-solar conditions, and accounting for dynamic feedbacks between interior and atmospheric processes. Exploration of the atmosphere and surface composition of individual, short-period super-Earths in the next few years will enable key inferences on magma ocean dynamics, the redox state of rocky planetary mantles, and mixing between volatile and refractory phases in planetary regimes that are absent from the present-day Solar System, and reminiscent of the conditions of the prebiotic Earth. The atmospheric characterization of climate diversity and the statistical search for biosignatures on terrestrial exoplanets on temperate orbits will require space-based direct imaging surveys, capable of resolving emission features of major and trace gases in both shortwave and mid-infrared wavelengths.

39 pages, 11 figures; review chapter accepted for publication in Treatise on Geochemistry, 3rd edition

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• Reduced gas accretion on super-Earths and ice giants
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• Reconnaissance of the TRAPPIST-1 exoplanet system in the Lyman-$\alpha$ line
• A secondary atmosphere on the rocky exoplanet 55 Cancri e
• The potential for Earth-mass planet formation around brown dwarfs
• A reassessment of the in situ formation of close-in super-Earths
• A Volcanic Hydrogen Habitable Zone
• Coreless Terrestrial Exoplanets
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• The Case and Context for Atmospheric Methane as an Exoplanet Biosignature
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• Rocky super-Earths or waterworlds: the interplay of planet migration, pebble accretion and disc evolution
• Reconciling Magma-Ocean Crystallization Models with the present-day Structure of the Earth's mantle
• A review of possible planetary atmospheres in the TRAPPIST-1 system
• Hydrodynamics of Embedded Planets' First Atmospheres. I. A Centrifugal Growth Barrier for 2D Flows
• The atmospheric circulation and climate of terrestrial planets orbiting Sun-like and M-dwarf stars over a broad range of planetary parameters
• Linking the Climate and Thermal Phase Curve of 55 Cancri e
• Phase transitions in MgSiO3 post-perovskite in super-Earth mantles
• Pebble-driven Planet Formation around Very Low-mass Stars and Brown Dwarfs
• Pebble-driven planet formation for TRAPPIST-1 and other compact systems
• The Exoplanet Radius Valley from Gas-driven Planet Migration and Breaking of Resonant Chains
• Distinguishing oceans of water from magma on mini-Neptune K2-18b
• Inefficient volatile loss from the Moon-forming disk: reconciling the giant impact hypothesis and a wet Moon
• Accretion and Evolution of ~2.5 Earth-mass Planets with Voluminous H/He Envelopes
• A Statistical Comparative Planetology Approach to the Hunt for Habitable Exoplanets and Life Beyond the Solar System
• Thermodynamics of Element Volatility and its Application to Planetary Processes
• GJ 367b: A dense ultra-short period sub-Earth planet transiting a nearby red dwarf star
• Hubble WFC3 Spectroscopy of the Habitable-zone Super-Earth LHS 1140 b
• Signatures of Strong Magnetization and Metal-Poor Atmosphere for a Neptune-Size Exoplanet
• The formation of mini-Neptunes
• Hydrogen dominated atmospheres on terrestrial mass planets: evidence, origin and evolution
• Why do M dwarfs have more transiting planets?
• GJ 1252b: A Hot Terrestrial Super-Earth With No Atmosphere
• The Role of N2 as a Geo-Biosignature for the Detection and Characterization of Earth-like Habitats
• Growth after the streaming instability: from planetesimal accretion to pebble accretion
• Detection of an Atmosphere on a Rocky Exoplanet
• Unveiling shrouded oceans on temperate sub-Neptunes via transit signatures of solubility equilibria vs. gas thermochemistry
• The Mega-MUSCLES Spectral Energy Distribution Of TRAPPIST-1
• The Occurrence Rate of Terrestrial Planets Orbiting Nearby Mid-to-late M Dwarfs from TESS Sectors 1-42
• Escape and fractionation of volatiles and noble gases from Mars-sized planetary embryos and growing protoplanets
• Are exoplanetesimals differentiated?
• GJ 367b is a dark, hot, airless sub-Earth
• How Deep Is the Ocean? Exploring the phase structure of water-rich sub-Neptunes
• Re-analysis of the 267-GHz ALMA observations of Venus: No statistically significant detection of phosphine
• Abundant atmospheric methane from volcanism on terrestrial planets is unlikely and strengthens the case for methane as a biosignature
• Predicted diversity in water content of terrestrial exoplanets orbiting M dwarfs
• The persistence of oceans on Earth-like planets: insights from the deep-water cycle
• Observability of Evaporating Lava Worlds
• Isotopic enrichment of forming planetary systems from supernova pollution
• Convective outgassing efficiency in planetary magma oceans: insights from computational fluid dynamics
• No hydrogen exosphere detected around the super-Earth HD97658 b
• Solubility of water in peridotite liquids and the prevalence of steam atmospheres on rocky planets
• No escaping helium from 55 Cnc e
• A Heavy Molecular Weight Atmosphere for the Super-Earth π Men c
• Redox hysteresis of super-Earth exoplanets from magma ocean circulation
• Carbonate-Silicate Cycle Predictions of Earth-like Planetary Climates and Testing the Habitable Zone Concept
• Thermodynamic and Energetic Limits on Continental Silicate Weathering Strongly Impact the Climate and Habitability of Wet, Rocky Worlds
• The Albedos of Kepler's Close-in super-Earths
• Two temperate Earth-mass planets orbiting the nearby star GJ1002
• To cool is to keep: Residual H/He atmospheres of super-Earths and sub-Neptunes
• Accretion of the earliest inner solar system planetesimals beyond the water-snowline
• Bioverse: A Comprehensive Assessment of the Capabilities of Extremely Large Telescopes to Probe Earth-like O${}_2$ Levels in Nearby Transiting Habitable Zone Exoplanets
• 3D modelling of the impact of stellar activity on tidally locked terrestrial exoplanets: atmospheric composition and habitability
• Tidal Heating and the Habitability of the TRAPPIST-1 Exoplanets
• Habitability of Earth-like stagnant lid planets: Climate evolution and recovery from snowball states
• Distinguishing between wet and dry atmospheres of TRAPPIST-1 e and f
• Arid or Cloudy: Characterizing the Atmosphere of the super-Earth 55 Cancri e using High-Resolution Spectroscopy
• A new and simple prescription for planet orbital migration and eccentricity damping by planet-disc interactions based on dynamical friction
• The high-energy environment and atmospheric escape of the mini-Neptune K2-18 b
• Ground-Based Transit Observations of the Super-Earth 55 Cnc e
• A cool runaway greenhouse without surface magma ocean
• Investigating the architecture and internal structure of the TOI-561 system planets with CHEOPS, HARPS-N and TESS
• Oxygen False Positives on Habitable Zone Planets Around Sun-Like Stars
• Carbon cycling and interior evolution of water-covered plate tectonics and stagnant lid planets
• Cloud formation in metal-rich atmospheres of hot super-Earths like 55 Cnc e and CoRot7b
• Modelling the atmosphere of lava planet K2-141b: implications for low and high resolution spectroscopy
• Steady State by Recycling prevents Premature Collapse of Protoplanetary Atmospheres
• Observing Isotopologue Bands in Terrestrial Exoplanet Atmospheres with the James Webb Space Telescope---Implications for Identifying Past Atmospheric and Ocean Loss
• Atmospheric Erosion by Giant Impacts onto Terrestrial Planets: A Scaling Law for any Speed, Angle, Mass, and Density
• Reduced atmospheres of post-impact worlds: The early Earth
• The distribution of volatile elements during rocky planet formation
• Low Albedo Surfaces of Lava Worlds
• Optical Transmission Spectroscopy of the Terrestrial Exoplanet LHS 3844b from 13 Ground-Based Transit Observations
• Atmosphere loss in planet-planet collisions
• Numerical solution of a non-linear conservation law applicable to the interior dynamics of partially molten planets
• The habitability of stagnant-lid Earths around dwarf stars
• The K2-3 system revisited: testing photoevaporation and core-powered mass loss with three small planets spanning the radius valley
• Understanding planetary context to enable life detection on exoplanets and test the Copernican principle
• A roadmap for the atmospheric characterization of terrestrial exoplanets with JWST
• Is ozone a reliable proxy for molecular oxygen? I. The O2-O3 relationship for Earth-like atmospheres
• Assessment of Isoprene as a Possible Biosignature Gas in Exoplanets with Anoxic Atmospheres
• Testing the Detectability of Extraterrestrial ${\mathrm{O}}_2$ with the ELTs using Real Data with Real Noise
• Composition of Terrestrial Exoplanet Atmospheres from Meteorite Outgassing Experiments
• Reflected spectroscopy of small exoplanets II: characterization of terrestrial exoplanets
• Near-infrared transmission spectrum of TRAPPIST-1 h using Hubble WFC3 G141 observations
• Reconstructing the size distribution of the primordial Main Belt
• Implications of atmospheric nondetections for Trappist-1 inner planets on atmospheric retention prospects for outer planets
• Revisiting the Iconic Spitzer Phase Curve of 55 Cancri e: Hotter Dayside, Cooler Nightside and Smaller Phase Offset
• Formation of aqua planets with water of nebular origin: Effects of water enrichment on the structure and mass of captured atmospheres of terrestrial planets
• A Solar System formation analogue in the Ophiuchus star-forming complex
• A Volatile-Poor Formation of LHS 3844b based on its Lack of Significant Atmosphere
• Low volcanic outgassing rates for a stagnant lid Archean Earth with graphite-saturated magmas
• Beyond runaway: initiation of the post-runaway greenhouse state on rocky exoplanets
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• Internal or external magma oceans in the earliest protoplanets -- perspectives from nitrogen and carbon fractionation
• MAGRATHEA: an open-source spherical symmetric planet interior structure code
• Keeping M-Earths Habitable in the Face of Atmospheric Loss by Sequestering Water in the Mantle
• Ultra Short Period Planets in K2 with companions: a double transiting system for EPIC 220674823
• A multi-wavelength look at the GJ 9827 system -- No evidence of extended atmospheres in GJ 9827 b and d from HST and CARMENES data
• Helium Enhanced Planets Along the Upper Edge of the Radius Valley
• The energy budget and figure of Earth during recovery from the Moon-forming giant impact
• Possible Atmospheric Diversity of Low Mass Exoplanets, some Central Aspects
• Forming super-Mercuries: The role of stellar abundances
• Hemispheric Tectonics on super-Earth LHS 3844b
• Lyman-alpha in the GJ 1132 System: Stellar Emission and Planetary Atmospheric Evolution
• Interior dynamics of super-Earth 55 Cancri e
• Rotational Spectral Unmixing of Exoplanets: Degeneracies between Surface Colors and Geography
• A transmission spectrum of the sub-Earth planet L98-59~b in 1.1-1.7 $\mu$m
• Migration and Growth of Protoplanetary Embryos II: Emergence of Proto-Gas-Giants Cores versus Super Earths' Progenitor
• Evolution and Spectral Response of a Steam Atmosphere for Early Earth with a coupled climate-interior model
• Bioverse: The Habitable Zone Inner Edge Discontinuity as an Imprint of Runaway Greenhouse Climates on Exoplanet Demographics
• Reduced late bombardment on rocky exoplanets around M-dwarfs
• Investigating the visible phase-curve variability of 55 Cnc e
• Where are the Water Worlds?: Self-Consistent Models of Water-Rich Exoplanet Atmospheres
• Behind the Mask: can HARMONI@ELT detect biosignatures in the reflected light of Proxima b?
• Hubble WFC3 Spectroscopy of the Rocky Planet L 98-59 b: No Evidence for a Cloud-Free Primordial Atmosphere
• Ions in the Thermosphere of Exoplanets: Observable Constraints Revealed by Innovative Laboratory Experiments
• A mineralogical reason why all exoplanets cannot be equally oxidising
• Detection of Paschen $\beta$ absorption in the atmosphere of KELT-9 b: A new window into the atmospheres of ultra-hot Jupiters
• Habitable planet formation around low-mass stars: Rapid accretion, rapid debris removal and the essential contribution of external giants
• Diversity of planetary systems in low-mass disks: Terrestrial-type planet formation and water delivery
• A Concise Treatise on Converting Stellar Mass Fractions to Abundances to Molar Ratios
• Thermal Evolution and magnetic history of rocky planets
• Rapid Formation of Exoplanetesimals Revealed by White Dwarfs
• Atmospheric Dynamics of a Near Tidally Locked Earth-Size Planet
• Atmospheric carbon depletion as a tracer of water oceans and biomass on temperate terrestrial exoplanets
• Observational constraints on the likelihood of ${}^{26}$Al in planet-forming environments
• Giant impacts stochastically change the internal pressures of terrestrial planets
• Lava World: Exoplanet Surfaces
• Atmospheric stability and collapse on tidally locked rocky planets
• Inferring Chemical Disequilibrium Biosignatures for Proterozoic Earth-Like Exoplanets
• Narrow loophole for H2-dominated atmospheres on habitable rocky planets around M dwarfs
• Rocky sub-Neptunes formed by pebble accretion: Rain of rocks from polluted envelopes
• Blue marble, stagnant lid: Could dynamic topography avert a waterworld?
• The energetic particle environment of a GJ 436 b-like planet
• CHEOPS and TESS view of the ultra-short period super-Earth TOI-561 b
• Constraining Background N2 Inventories on Directly Imaged Terrestrial Exoplanets to Rule Out O2 False Positives
• The influence of surface $C{O}_2$ condensation on the evolution of warm and cold rocky planets orbiting Sun-like stars
• Salty ice and the dilemma of ocean exoplanet habitability
• Rapid-then-slow migration reproduces mass distribution of TRAPPIST-1 system
• Thermal evolution of rocky exoplanets with a graphite outer shell
• Short-lived radioisotope enrichment in star-forming regions from stellar winds and supernovae
• Imaging of exocomets with infrared interferometry
• Planet formation and disk mass dependence in a pebble-driven scenario for low mass stars
• Diverse Carbonates in Exoplanet Oceans Promote the Carbon Cycle
• Observations of planetary winds and outflows
• Detecting Atmospheric Molecules of Temperate Terrestrial Exoplanets using High-Resolution Spectroscopy in the Mid Infrared Domain

Cited by in corpus (18)

• Escaping Helium and a Highly Muted Spectrum Suggest a Metal-Enriched Atmosphere on Sub-Neptune GJ3090b from JWST Transit Spectroscopy
• Magma ocean evolution at arbitrary redox state
• JWST COMPASS: NIRSpec/G395H Transmission Observations of the Super-Earth TOI-776b
• Convective shutdown in the atmospheres of lava worlds
• Magma ocean interactions can explain JWST observations of the sub-Neptune TOI-270 d
• Prospects for Detecting Signs of Life on Exoplanets in the JWST Era
• Constraining exoplanet interiors using observations of their atmospheres
• Self-limited tidal heating and prolonged magma oceans in the L 98-59 system
• Characterisation of TOI-406 as showcase of the THIRSTEE program: A 2-planet system straddling the M-dwarf density gap
• The JWST Rocky Worlds DDT Program reveals GJ 3929b to likely be a bare rock
• Two neighbours of the ultra-short-period Earth-sized planet K2-157 b in the warm Neptunian savanna
• Absence of a Runaway Greenhouse Limit on Lava Planets
• AGNI: A radiative-convective model for lava planet atmospheres
• Probing the Limits of Habitability: A Catalog of Rocky Exoplanets in the Habitable Zone
• The dark and featureless surface of rocky exoplanet LHS 3844 b from JWST mid-infrared spectroscopy
• Not Earth-like Yet Temperate? More Generic Climate Feedback Configurations Still Allow Temperate Climates in Habitable Zone Exo-Earth Candidates
• Impact of rotation on synthetic mass-radius relationships of two-layer rocky planets and water worlds
• What the Solar System Can Teach Us About Rocky Exoplanets