The Exoplanet Perspective on Future Ice Giant Exploration

Abstract

Exoplanets number in their thousands, and the number is ever increasing with the advent of new surveys and improved instrumentation. One of the most surprising things we have learnt from these discoveries is not that small-rocky planets in their stars habitable zones are likely common, but that the most typical size of exoplanet is that not seen in our solar system - radii between that of Neptune and the Earth dubbed mini-Neptunes and super-Earths. In fact, a transiting exoplanet is four times as likely to be in this size regime than that of any giant planet in our solar system. Investigations into the atmospheres of giant hydrogen/helium dominated exoplanets has pushed down to Neptune and mini-Neptune sized worlds revealing molecular absorption from water, scattering and opacity from clouds, and measurements of atmospheric abundances. However, unlike measurements of Jupiter, or even Saturn sized worlds, the smaller giants lack a ground truth on what to expect or interpret from their measurements. How did these sized worlds form and evolve and was it different from their larger counterparts? What is their internal composition and how does that impact their atmosphere? What informs the energy budget of these distant worlds? In this we discuss what characteristics we can measure for exoplanets, and why a mission to the ice giants in our solar system is the logical next step for understanding exoplanets.

arXiv commentreview paper accepted in Philos. Trans. R. Soc. A. 5 figures, 14 pages

References in corpus (51)

• The effects of snowlines on C/O in planetary atmospheres
• Clouds in the atmosphere of the super-Earth exoplanet GJ 1214b
• Growth Model Interpretation of Planet Size Distribution
• Homogeneous studies of transiting extrasolar planets. IV. Thirty systems with space-based light curves
• The California Kepler Survey VII. Precise Planet Radii Leveraging Gaia DR2 Reveal the Stellar Mass Dependence of the Planet Radius Gap
• Comparing Jupiter interior structure models to Juno gravity measurements and the role of a dilute core
• A featureless transmission spectrum for the Neptune-mass exoplanet GJ 436b
• The Effect of Condensates on the Characterization of Transiting Planet Atmospheres with Transmission Spectroscopy
• Chemical consequences of the C/O ratio on hot Jupiters: Examples from WASP-12b,CoRoT-2b, XO-1b, and HD 189733b
• Interior Models of Uranus and Neptune
• A Sub-Neptune Exoplanet with a Low-Metallicity Methane-Depleted Atmosphere and Mie-Scattering Clouds
• Aerosol Composition of Hot Giant Exoplanets Dominated by Silicates and Hydrocarbon Hazes
• The Influence of Non-Uniform Cloud Cover on Transit Transmission Spectra
• New indication for a dichotomy in the interior structure of Uranus and Neptune from the application of modified shape and rotation data
• Global Climate and Atmospheric Composition of the Ultra-Hot Jupiter WASP-103b from HST and Spitzer Phase Curve Observations
• HAT-P-26b: A Neptune-Mass Exoplanet with a Well Constrained Heavy Element Abundance
• Hubble Space Telescope Near-IR Transmission Spectroscopy of the Super-Earth HD 97658b
• The Optical and Near-Infrared Transmission Spectrum of the Super-Earth GJ1214b: Further Evidence for a Metal-Rich Atmosphere
• Spitzer Phase Curve Constraints for WASP-43b at 3.6 and 4.5 microns
• The Complete transmission spectrum of WASP-39b with a precise water constraint
• Forward and Inverse Modeling of the Emission and Transmission Spectrum of GJ 436b: Investigating Metal Enrichment, Tidal Heating, and Clouds
• Trends in Atmospheric Properties of Neptune-Size Exoplanets
• Connecting Giant Planet Atmosphere and Interior Modeling: Constraints on Atmospheric Metal Enrichment
• A framework to combine low- and high-resolution spectroscopy for the atmospheres of transiting exoplanets
• The Impact of Non-Uniform Thermal Structure on the Interpretation of Exoplanet Emission Spectra
• Why is it so Cold in Here?: Explaining the Cold Temperatures Retrieved from Transmission Spectra of Exoplanet Atmospheres
• An Updated Study of Potential Targets for Ariel
• Methane on Uranus: The case for a compact CH4 cloud layer at low latitudes and a severe CH4 depletion at high-latitudes based on re-analysis of Voyager occultation measurements and STIS spectroscopy
• Titan solar occultation observations reveal transit spectra of a hazy world
• Transit Signatures of Inhomogeneous Clouds on Hot Jupiters: Insights From Microphysical Cloud Modeling
• A HST/WFC3 Thermal Emission Spectrum of the Hot Jupiter HAT-P-7b
• Glancing views of the Earth. From a lunar eclipse to an exoplanetary transit
• Understanding and Mitigating Biases when Studying Inhomogeneous Emission Spectra with JWST
• Dust Ablation on the Giant Planets: Consequences for Stratospheric Photochemistry
• An emission spectrum for WASP-121b measured across the 0.8-1.1 micron wavelength range using the Hubble Space Telescope
• Deep Atmosphere Composition, Structure, Origin, and Exploration, with Particular Focus on Critical in situ Science at the Icy Giants
• The Structure of Exoplanets
• The Formation of Uranus & Neptune: Challenges and Implications For Intermediate-Mass Exoplanets
• Bifurcation in the history of Uranus and Neptune: the role of giant impacts
• Telling twins apart: Exo-Earths and Venuses with transit spectroscopy
• A Hubble PanCET Study of HAT-P-11b: A Cloudy Neptune with a Low Atmospheric Metallicity
• Collisional stripping of planetary crusts
• WASP-52b. The effect of starspot correction on atmospheric retrievals
• Fully scalable forward model grid of exoplanet transmission spectra
• Exoplanet Atmospheres at High Spectral Resolution
• Saturn's Probable Interior: An Exploration of Saturn's Potential Interior Density Structures
• Atmosphere loss in planet-planet collisions
• The Transit Transmission Spectrum of a Cold Gas Giant Planet
• The Transit Spectra of Earth and Jupiter
• Key Atmospheric Signatures for Identifying the Source Reservoirs of Volatiles in Uranus and Neptune
• Exoplanet Atmosphere Measurements from Direct Imaging

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• The nature and origins of sub-Neptune size planets
• Nitrogen as a Tracer of Giant Planet Formation. I.: A Universal Deep Adiabatic Profile and Semi-analytical Predictions of Disequilibrium Ammonia Abundances in Warm Exoplanetary Atmospheres
• The metal-poor atmosphere of a Neptune/Sub-Neptune planet progenitor
• Ice Giant System Exploration in the 2020s: An Introduction
• ACCESS: Confirmation of a Clear Atmosphere for WASP-96b and a Comparison of Light Curve Detrending Techniques
• Planet Mass and Metallicity: The Exoplanets and Solar System Connection
• Dynamics and Clouds in Planetary Atmospheres from Telescopic Observations
• The Effect of Metallicity on the Non-Equilibrium Abundance of Hydrogen Dominated Exoplanet Atmosphere
• Kilometer-precise (UII) Umbriel physical properties from the multichord stellar occultation on 2020 September 21
• On the Utility of Transmission Color Analysis I: Differentiating Super-Earths and Sub-Neptunes
• The Dynamical Viability of an Extended Jupiter Ring System