Extreme hydrodynamic atmospheric loss near the critical thermal escape regime

Еркаев, Н. В.; Lämmer, H.; Odert, P.; Kulikov, Yu. N.; Kislyakova, K. G.

doi:10.1093/mnras/stv130

Cited by 45 publications

(50 citation statements)

References 29 publications

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“…The dotted parts of the lines show the regions where the Knudsen number (defined here using Equations (3)-(5) of Erkaev et al 2015) is greater than unity, and therefore the simulations are not reliable (the top of the solid line therefore shows the exobase). In the velocity plot, the dashed line is the escape velocity and the circles show where the wind becomes supersonic.…”

Section: Results: the Importance Of Stellar Rotational Evolutionmentioning

confidence: 99%

“…We integrate the input XUV flux downwards through the atmosphere by decreasing the radiation flux by a factor of e t -when traveling through each grid cell, where τ=nσds, ds is the grid cell thickness, and n is the hydrogen atom number density. The heating of the gas within each grid cell is given by q=òσnF XUV , where F XUV is in this case the XUV flux in the grid cell and ò=0.15 is the heating efficiency parameter (Shematovich et al 2014;Erkaev et al 2015;Ionov & Shematovich 2015).…”

Section: Atmospheric Mass Loss and The F Xuv Dependencementioning

confidence: 99%

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The Evolution of Stellar Rotation and the Hydrogen Atmospheres of Habitable-Zone Terrestrial Planets

Johnstone

Güdel

Stökl

et al. 2015

ApJ

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147

138

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Terrestrial planets formed within gaseous protoplanetary disks can accumulate significant hydrogen envelopes. The evolution of such an atmosphere due to XUV driven evaporation depends on the activity evolution of the host star, which itself depends sensitively on its rotational evolution, and therefore on its initial rotation rate. In this Letter, we derive an easily applicable method for calculating planetary atmosphere evaporation that combines models for a hydrostatic lower atmosphere and a hydrodynamic upper atmosphere. We show that the initial rotation rate of the central star is of critical importance for the evolution of planetary atmospheres and can determine if a planet keeps or loses its primordial hydrogen envelope. Our results highlight the need for a detailed treatment of stellar activity evolution when studying the evolution of planetary atmospheres.

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Section: Results: the Importance Of Stellar Rotational Evolutionmentioning

confidence: 99%

Section: Atmospheric Mass Loss and The F Xuv Dependencementioning

confidence: 99%

The Evolution of Stellar Rotation and the Hydrogen Atmospheres of Habitable-Zone Terrestrial Planets

Johnstone

Güdel

Stökl

et al. 2015

ApJ

Self Cite

147

138

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“…where R XUV eff is the effective radius at which the XUV energy is absorbed in the upper atmosphere (see Table 1; Erkaev et al 2007Erkaev et al , 2015 and η is the heating efficiency (see Sect. 2.1).…”

Section: Using Escape Rates To Identify Planets In the Boil-off Regimementioning

confidence: 99%

Aeronomical constraints to the minimum mass and maximum radius of hot low-mass planets

Fossati

Еркаев

Lämmer

et al. 2017

A&A

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113

105

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Stimulated by the discovery of a number of close-in low-density planets, we generalise the Jeans escape parameter taking hydrodynamic and Roche lobe effects into account. We furthermore define Λ as the value of the Jeans escape parameter calculated at the observed planetary radius and mass for the planet's equilibrium temperature and considering atomic hydrogen, independently of the atmospheric temperature profile. We consider 5 and 10 M ⊕ planets with an equilibrium temperature of 500 and 1000 K, orbiting early G-, K-, and M-type stars. Assuming a clear atmosphere and by comparing escape rates obtained from the energy-limited formula, which only accounts for the heating induced by the absorption of the high-energy stellar radiation, and from a hydrodynamic atmosphere code, which also accounts for the bolometric heating, we find that planets whose Λ is smaller than 15-35 lie in the "boiloff" regime, where the escape is driven by the atmospheric thermal energy and low planetary gravity. We find that the atmosphere of hot (i.e. T eq 1000 K) low-mass (M pl 5 M ⊕ ) planets with Λ < 15-35 shrinks to smaller radii so that their Λ evolves to values higher than 15-35, hence out of the boil-off regime, in less than ≈500 Myr. Because of their small Roche lobe radius, we find the same result also for hot (i.e. T eq 1000 K) higher mass (M pl 10 M ⊕ ) planets with Λ < 15-35, when they orbit M-dwarfs. For old, hydrogen-dominated planets in this range of parameters, Λ should therefore be ≥15-35, which provides a strong constraint on the planetary minimum mass and maximum radius and can be used to predict the presence of aerosols and/or constrain planetary masses, for example.

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“…Here, J m (r, θ) is a function in spherical coordinates describing the spatial variation of the EUV, or X-ray, flux due to atmospheric absorption (Erkaev et al 2015) and r in this case is radial distance from the planetary centre, in units of R pl . Following Murray-Clay et al (2009), the absorption cross-sections are given by σ = σ 0 (…”

Section: Physical Modelmentioning

confidence: 99%

“…(20), J XUV corresponds to the stellar XUV flux inside the atmosphere, which depends on r and on the spherical angle (see Erkaev et al 2007Erkaev et al , 2015, for more details). The R eff values correspond roughly to the positions of the temperature maxima shown in Fig.…”

Section: Atmospheric Escape Regimementioning

confidence: 99%

Young planets under extreme UV irradiation

Kubyshkina

Lendl

Fossati

et al. 2018

A&A

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The K2-33 planetary system hosts one transiting ∼5 R⊕ planet orbiting the young M-type host star. The planet's mass is still unknown, with an estimated upper limit of 5.4 MJ . The extreme youth of the system (<20 Myr) gives the unprecedented opportunity to study the earliest phases of planetary evolution, at a stage when the planet is exposed to an extremely high level of high-energy radiation emitted by the host star. We perform a series of 1D hydrodynamic simulations of the planet's upper atmosphere considering a range of possible planetary masses, from 2 to 40 M⊕, and equilibrium temperatures, from 850 to 1300 K, to account for internal heating as a result of contraction. We obtain temperature profiles mostly controlled by the planet's mass, while the equilibrium temperature has a secondary effect. For planetary masses below 7-10 M⊕, the atmosphere is subject to extremely high escape rates, driven by the planet's weak gravity and high thermal energy, which increase with decreasing mass and/or increasing temperature. For higher masses, the escape is instead driven by the absorption of the high-energy stellar radiation. A rough comparison of the timescales for complete atmospheric escape and age of the system indicates that the planet is more massive than 10 M⊕.

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Extreme hydrodynamic atmospheric loss near the critical thermal escape regime

Cited by 45 publications

References 29 publications

The Evolution of Stellar Rotation and the Hydrogen Atmospheres of Habitable-Zone Terrestrial Planets

The Evolution of Stellar Rotation and the Hydrogen Atmospheres of Habitable-Zone Terrestrial Planets

Aeronomical constraints to the minimum mass and maximum radius of hot low-mass planets

Young planets under extreme UV irradiation

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