Blowin' in the non-isothermal wind: core-powered mass loss with hydrodynamic radiative transfer
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| Format: | Preprint |
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2024
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| _version_ | 1866929708304695296 |
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| author | Misener, William Schulik, Matthäus Schlichting, Hilke E. Owen, James E. |
| author_facet | Misener, William Schulik, Matthäus Schlichting, Hilke E. Owen, James E. |
| contents | The mass loss rates of planets undergoing core-powered escape are usually modeled using an isothermal Parker-type wind at the equilibrium temperature, $T_\mathrm{eq}$. However, the upper atmospheres of sub-Neptunes may not be isothermal if there are significant differences between the opacity to incident visible and outgoing infrared radiation. We model bolometrically-driven escape using aiolos, a hydrodynamic radiative-transfer code that incorporates double-gray opacities, to investigate the process's dependence on the visible-to-infrared opacity ratio, $γ$. For a value of $γ\approx 1$, we find that the resulting mass loss rates are well-approximated by a Parker-type wind with an isothermal temperature $T = T_\mathrm{eq}/2^{1/4}$. However, we show that over a range of physically plausible values of $γ$, the mass loss rates can vary by orders of magnitude, ranging from $10^{-5} \times$ the isothermal rate for low $γ$ to $10^5 \times$ the isothermal rate for high $γ$. The differences in mass loss rates are largest for small planet radii, while for large planet radii, mass loss rates become nearly independent of $γ$ and approach the isothermal approximation. We incorporate these opacity-dependent mass loss rates into a self-consistent planetary mass and energy evolution model and show that lower/higher $γ$ values lead to more/less hydrogen being retained after core-powered mass loss. In some cases, the choice of opacities determines whether or not a planet can retain a significant primordial hydrogen atmosphere. The dependence of escape rate on the opacity ratio may allow atmospheric escape observations to directly constrain a planet's opacities and therefore its atmospheric composition. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2405_15221 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | Blowin' in the non-isothermal wind: core-powered mass loss with hydrodynamic radiative transfer Misener, William Schulik, Matthäus Schlichting, Hilke E. Owen, James E. Earth and Planetary Astrophysics The mass loss rates of planets undergoing core-powered escape are usually modeled using an isothermal Parker-type wind at the equilibrium temperature, $T_\mathrm{eq}$. However, the upper atmospheres of sub-Neptunes may not be isothermal if there are significant differences between the opacity to incident visible and outgoing infrared radiation. We model bolometrically-driven escape using aiolos, a hydrodynamic radiative-transfer code that incorporates double-gray opacities, to investigate the process's dependence on the visible-to-infrared opacity ratio, $γ$. For a value of $γ\approx 1$, we find that the resulting mass loss rates are well-approximated by a Parker-type wind with an isothermal temperature $T = T_\mathrm{eq}/2^{1/4}$. However, we show that over a range of physically plausible values of $γ$, the mass loss rates can vary by orders of magnitude, ranging from $10^{-5} \times$ the isothermal rate for low $γ$ to $10^5 \times$ the isothermal rate for high $γ$. The differences in mass loss rates are largest for small planet radii, while for large planet radii, mass loss rates become nearly independent of $γ$ and approach the isothermal approximation. We incorporate these opacity-dependent mass loss rates into a self-consistent planetary mass and energy evolution model and show that lower/higher $γ$ values lead to more/less hydrogen being retained after core-powered mass loss. In some cases, the choice of opacities determines whether or not a planet can retain a significant primordial hydrogen atmosphere. The dependence of escape rate on the opacity ratio may allow atmospheric escape observations to directly constrain a planet's opacities and therefore its atmospheric composition. |
| title | Blowin' in the non-isothermal wind: core-powered mass loss with hydrodynamic radiative transfer |
| topic | Earth and Planetary Astrophysics |
| url | https://arxiv.org/abs/2405.15221 |