Role of Planetary Radius on Atmospheric Escape of Rocky Exoplanets

Abstract

Large-scale characterization of exoplanetary atmospheres is on the horizon, thereby making it possible in the future to extract their statistical properties. In this context, by using a well validated model in the solar system, we carry out three-dimensional magnetohydrodynamic simulations to compute nonthermal atmospheric ion escape rates of unmagnetized rocky exoplanets as a function of their radius based on fixed stellar radiation and wind conditions. We find that the atmospheric escape rate is, unexpectedly and strikingly, a nonmonotonic function of the planetary radius $R$ and that it evinces a maximum at $R\sim 0.7R_{\oplus }$. This novel nonmonotonic behavior may arise from an intricate tradeoff between the cross-sectional area of a planet (which increases with size, boosting escape rates) and its associated escape velocity (which also increases with size, but diminishes escape rates). Our results could guide forthcoming observations because worlds with certain values of $R$ (such as $R\sim 0.7R_{\oplus }$) might exhibit comparatively higher escape rates when all other factors are constant.

8 pages, 2 figures, 2 tables; to appear in The Astrophysical Journal Letters

References in corpus (30)

• Habitable Zones Around Main-Sequence Stars: Dependence on Planetary Mass
• Growth Model Interpretation of Planet Size Distribution
• The James Webb Space Telescope Mission
• Roche lobe effects on the atmospheric loss of "Hot Jupiters"
• Revisited Mass-Radius relations for exoplanets below 120 Earth masses
• Thermal emission from the Earth-sized exoplanet TRAPPIST-1 b using JWST
• No thick carbon dioxide atmosphere on the rocky exoplanet TRAPPIST-1 c
• The Gaia-Kepler Stellar Properties Catalog. II. Planet Radius Demographics as a Function of Stellar Mass and Age
• Is Proxima Centauri b habitable? -- A study of atmospheric loss
• The nature and origins of sub-Neptune size planets
• A JWST transmission spectrum of a nearby Earth-sized exoplanet
• New Observational Constraints on the Winds of M Dwarf Stars
• Atmospheric Escape Processes and Planetary Atmospheric Evolution
• Planetary evolution with atmospheric photoevaporation I. Analytical derivation and numerical study of the evaporation valley and transition from super-Earths to sub-Neptunes
• A Spectroscopic Analysis of the California-Kepler Survey Sample: I. Stellar Parameters, Planetary Radii and a Slope in the Radius Gap
• Photoevaporation vs. core-powered mass-loss: model comparison with the 3D radius gap
• Atmospheric Regimes and Trends on Exoplanets and Brown Dwarfs
• Atmospheres of Rocky Exoplanets
• Chemical Fingerprints of Formation in Rocky Super-Earths' Data
• Planetary Magnetic Field Control of Ion Escape from Weakly Magnetized Planets
• The sub-Neptune desert and its dependence on stellar type: Controlled by lifetime X-ray irradiation
• The dehydration of water worlds via atmospheric losses
• Atmospheric Escape From TOI-700 d: Venus versus Earth Analogs
• A critical assessment of the applicability of the energy-limited approximation for estimating exoplanetary mass-loss rates
• Evidence of energy-, recombination-, and photon-limited escape regimes in giant planet H/He atmospheres
• The Demographics of Terrestrial Planets in the Venus Zone
• Planetary Magnetism as a Parameter in Exoplanet Habitability
• Atmospheric Dynamics of a Near Tidally Locked Earth-Size Planet
• Revisiting the Biological Ramifications of Variations in Earth's Magnetic Field
• Non-thermal escape of the Martian CO${}_2$ atmosphere over time: constrained by Ar isotopes

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• Radio prospects of extrasolar aurorae polaris as a probe of planetary magnetism
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