Mapping out the parameter space for photoevaporation and core-powered mass-loss

2023/07/31 by James E. Owen, Hilke E. Schlichting, Owen, James E. +1 · 1 voice · 11 citations
Physics and Astronomy · #Earth and Planetary Astrophysics (astro-ph.EP) #FOS: Physical sciences #astro-ph.EP

paper · pdf · doi:10.48550/arxiv.2308.00020

arxiv published 2023/07/31 · arxiv updated 2023/12/21

Abstract

Understanding atmospheric escape in close-in exoplanets is critical to interpreting their evolution. We map out the parameter space over which photoevaporation and core-powered mass loss dominate atmospheric escape. Generally, the transition between the two regimes is determined by the location of the Bondi radius (i.e. the sonic point of core-powered outflow) relative to the penetration depth of XUV photons. Photoevaporation dominates the loss when the XUV penetration depth lies inside the Bondi radius (R_XUV<R_B) and core-powered mass-loss when XUV radiation is absorbed higher up in the flow (R_B<R_XUV). The transition between the two regimes occurs at a roughly constant ratio of the planet's radius to its Bondi radius, with the exact value depending logarithmically on planetary and stellar properties. In general, core-powered mass-loss dominates for lower-gravity planets with higher equilibrium temperatures, and photoevaporation dominates for higher-gravity planets with lower equilibrium temperatures. However, planets can transition between these two mass-loss regimes during their evolution, and core-powered mass loss can ``enhance'' photo-evaporation over a significant region of parameter space. Interestingly, a planet that is ultimately stripped by core-powered mass-loss has likely only ever experienced core-powered mass-loss. In contrast a planet that is ultimately stripped by photoevaporation could have experienced an early phase of core-powered mass-loss. Applying our results to the observed super-Earth population suggests that it contains significant fractions of planets where each mechanism controlled the final removal of the H/He envelope, although photoevaporation appears to be responsible for the final carving of the exoplanet radius-valley.

Cited by

• X-ray Evolution of Young Stars: Early Dimming and Coronal Softening in Solar-Mass Stars with Implications for Planetary Atmospheres
• Fundamentals of interior modelling and challenges in the interpretation of observed rocky exoplanets
• Are We There Yet? Challenges in Quantifying the Frequency of Earth Analogs in the Habitable Zone
• Wind-AE: A Fast, Open-source 1D Photoevaporation Code with Metal and Multi-frequency X-ray Capabilities
• The cosmochemistry of planetary systems
• Understanding the Origins of Super-Puff Planets: A New Mass-Loss Regime Coupled to Planetary Evolution
• VIPER: A high-resolution multimode fiber-fed VIPA spectrograph concept for characterizing exoplanet atmospheric escape
• Modeling tails of escaping gas in exoplanet atmospheres with Harmonica
• The Orbital Eccentricity-Radius Relation for Planets Orbiting M Dwarfs
• Diversity of low-mass planet atmospheres in the C-H-O-N-S-Cl system with interior dissolution, nonideality, and condensation: Application to TRAPPIST-1e and sub-Neptunes
• The Cosmic Shoreline Revisited: A Metric for Atmospheric Retention Informed by Hydrodynamic Escape

Discussions

• Next up, Owen & Schlichting have their newest model of atmosphere loss from #exoplanets. https://arxiv.org/abs/2308.00020 The details are kind of finicky, but this is one of the best models I've seen [bsky, 0 points, 0 comments]

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