Mass loss by atmospheric escape from extremely close-in planets

Abstract

We explore atmospheric escape from close-in exoplanets with the highest mass loss rates. First, we locate the transition from stellar X-ray and UV-driven escape to rapid Roche lobe overflow, which occurs once the 10-100 nbar pressure level in the atmosphere reaches the Roche lobe. Planets enter this regime when the ratio of the substellar radius to the polar radius along the visible surface pressure level, that aligns with a surface of constant Roche potential, is X/Z~$\gtrsim$~1.2 for Jovian planets (Mp~$\gtrsim$~100 M$_{\Earth}$) and X/Z~$\gtrsim$~1.02 for sub-Jovian planets ($M_p\approx$~10--100 M$_{\Earth}$). Around a sun-like star, this regime applies to orbital periods of less than two days for planets with radii of about 3--14 R$_{\Earth}$. Our results agree with the properties of known transiting planets and can explain parts of the sub-Jovian desert in the population of known exoplanets. Second, we present detailed numerical simulations of atmospheric escape from a planet like Uranus or Neptune orbiting close to a sun-like star that support the results above and point to interesting qualitative differences between hot Jupiters and sub-Jovian planets. We find that hot Neptunes with solar metallicity hydrogen and helium envelopes have relatively more extended upper atmospheres than typical hot Jupiters, with a lower ionization fraction and higher abundances of escaping molecules. This is consistent with existing ultraviolet transit observations of warm Neptunes and it might provide a way to use future observations and models to distinguish solar metallicity atmospheres from higher metallicity atmospheres.

arXiv commentAccepted to Astrophysical Journal

References in corpus (65)

• The California-Kepler Survey. III. A Gap in the Radius Distribution of Small Planets
• Evolution of the Solar Activity over Time and Effects on Planetary Atmospheres: I. High-energy Irradiances (1-1700 A)
• The evaporation valley in the Kepler planets
• Atmospheric Escape from Hot Jupiters
• Probabilistic Forecasting of the Masses and Radii of Other Worlds
• A giant comet-like cloud of hydrogen escaping the warm Neptune-mass exoplanet GJ 436b
• Disequilibrium Carbon, Oxygen, and Nitrogen Chemistry in the Atmospheres of HD 189733b and HD 209458b
• Roche lobe effects on the atmospheric loss of "Hot Jupiters"
• Giant Planets at Small Orbital Distances
• How Thermal Evolution and Mass Loss Sculpt Populations of Super-Earths and Sub-Neptunes: Application to the Kepler-11 System and Beyond
• Helium in the eroding atmosphere of an exoplanet
• Dearth of short-period Neptunian exoplanets - a desert in period-mass and period-radius planes
• Metals in the Exosphere of the Highly Irradiated Planet WASP-12b
• Observations of Mass Loss from the Transiting Exoplanet HD 209458b
• Revised Radii of Kepler Stars and Planets Using Gaia Data Release 2
• Homogeneous studies of transiting extrasolar planets. III. Additional planets and stellar models
• Atmospheric Chemistry in Giant Planets, Brown Dwarfs, and Low-Mass Dwarf Stars II. Sulfur and Phosphorus
• Atmospheric Escape from Hot Jupiters
• A Study of the Shortest-Period Planets Found With Kepler
• Temporal variations in the evaporating atmosphere of the exoplanet HD 189733b
• The escape of heavy atoms from the ionosphere of HD209458b. I. A photochemical-dynamical model of the thermosphere
• WASP-121 b: a hot Jupiter in a polar orbit and close to tidal disruption
• Signatures of the Core-Powered Mass-Loss Mechanism in the Exoplanet Population: Dependence on Stellar Properties and Observational Predictions
• Hubble PanCET: An extended upper atmosphere of neutral hydrogen around the warm Neptune GJ 3470 b
• First astrophysical detection of the helium hydride ion (HeH${}^{+}$)
• The HST PanCET Program: Exospheric Mg II and Fe II in the Near-UV transmission spectrum of WASP-121b using Jitter Decorrelation
• Star formation at very low metallicity. I: Chemistry and cooling at low densities
• Born Dry in the Photo-Evaporation Desert: Kepler's Ultra-Short-Period Planets Formed Water-Poor
• WASP-12b as a prolate, inflated and disrupting planet from tidal dissipation
• Classification of magnetized star--planet interactions: bow shocks, tails, and inspiraling flows
• Magnetically controlled mass loss from extrasolar planets in close orbits
• Hot Jupiter Magnetospheres
• Mass Transfer, Transiting Stream and Magnetopause in Close-in Exoplanetary Systems with Applications to WASP-12
• Overcoming the limitations of the energy-limited approximation for planet atmospheric escape
• Magnetospheric Structure and Atmospheric Joule Heating of Habitable Planets Orbiting M-dwarf Stars
• Structure and Composition of Pluto's atmosphere from the New Horizons Solar Ultraviolet Occultation
• Hubble Space Telescope detection of oxygen in the atmosphere of exoplanet HD189733b
• On the diversity of magnetic interactions in close-in star-planet systems
• The escape of heavy atoms from the ionosphere of HD209458b. II. Interpretation of the observations
• Physical properties, transmission and emission spectra of the WASP-19 planetary system from multi-colour photometry
• Detection of Helium in the Atmosphere of the Exo-Neptune HAT-P-11b
• Absorbing gas around the WASP-12 planetary system
• Transit Timing Variation Measurements of WASP-12b and Qatar-1b: No Evidence for Additional Planets
• Mass-Loss Evolution of Close-In Exoplanets: Evaporation of Hot Jupiters and the Effect on Population
• NGTS-4b: A sub-Neptune Transiting in the Desert
• Hydrogen dominated atmospheres on terrestrial mass planets: evidence, origin and evolution
• Rapid escape of ultra-hot exoplanet atmospheres driven by Hydrogen Balmer absorption
• OGLE2-TR-L9: An extrasolar planet transiting a fast-rotating F3 star
• Photochemical hazes in sub-Neptunian atmospheres with focus on GJ 1214 b
• A Model of the H$\alpha$ and Na Transmission Spectrum of HD 189733b
• A New Model of Roche-lobe Overflow for Short-Period Gaseous Planets and Binary Stars
• Escaping particle fluxes in the atmospheres of close-in exoplanets. ii. reduced mass loss rates and anisotropic winds
• A Compact Multi-Planet System With A Significantly Misaligned Ultra Short Period Planet
• 3D Aeronomy Modeling of Close-in Exoplanets
• Ultraviolet C II and Si III Transit Spectroscopy and Modeling of the Evaporating Atmosphere of GJ436b
• Impact of photochemical hazes and gases on exoplanet atmospheric thermal structure
• Effect of stellar flares on the upper atmospheres of HD 189733b and HD 209458b
• Detection of vibrational emissions from the helium hydride ion (HeH${}^{+}$) in the planetary nebula NGC 7027
• Thermal escape from extrasolar giant planets
• Unmasking the hidden NGTS-3Ab: a hot Jupiter in an unresolved binary system
• TOI-132 b: A short-period planet in the Neptune desert transiting a $V=11.3$ G-type star
• EUV-driven ionospheres and electron transport on extrasolar giant planets orbiting active stars
• The Upper Atmosphere of HD17156b
• Orbital period modulation in hot Jupiter systems
• On the escape of CH4 from Pluto's atmosphere

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