Hydrodynamics of embedded planets’ first atmospheres – II. A rapid recycling of atmospheric gas

Ormel, Chris W.; Shi, Ji-Ming; Kuiper, Rolf

doi:10.1093/mnras/stu2704

Cited by 188 publications

(236 citation statements)

References 42 publications

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“…With mesh refinement applied only to the vicinity of the core, it would be possible to more reliably determine the fate of more strongly coupled particles (for applications toward smaller disk radii, millimetercentimeter sized pebbles already become strongly coupled with τ s 0.01). In particular, in the vicinity of embedded planetary cores, complex 3D flow structures have been found on the scale of the core's Bondi radius (Ormel et al 2015;Fung et al 2015), which may affect the accretion of strongly coupled particles.…”

Section: Summary and Discussionmentioning

confidence: 99%

Pebble Accretion in Turbulent Protoplanetary Disks

Bai

Murray-Clay

2017

ApJ

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It has been realized in recent years that the accretion of pebble-sized dust particles onto planetary cores is an important mode of core growth, which enables the formation of giant planets at large distances and assists planet formation in general. The pebble accretion theory is built upon the orbit theory of dust particles in a laminar protoplanetary disk (PPD). For sufficiently large core mass (in the "Hill regime"), essentially all particles of appropriate sizes entering the Hill sphere can be captured. However, the outer regions of PPDs are expected to be weakly turbulent due to the magnetorotational instability (MRI), where turbulent stirring of particle orbits may affect the efficiency of pebble accretion. We conduct shearing-box simulations of pebble accretion with different levels of MRI turbulence (strongly turbulent assuming ideal magnetohydrodynamics, weakly turbulent in the presence of ambipolar diffusion, and laminar) and different core masses to test the efficiency of pebble accretion at a microphysical level. We find that accretion remains efficient for marginally coupled particles (dimensionless stopping time τ s ∼ 0.1 − 1) even in the presence of strong MRI turbulence. Though more dust particles are brought toward the core by the turbulence, this effect is largely canceled by a reduction in accretion probability. As a result, the overall effect of turbulence on the accretion rate is mainly reflected in the changes in the thickness of the dust layer. On the other hand, we find that the efficiency of pebble accretion for strongly coupled particles (down to τ s ∼ 0.01) can be modestly reduced by strong turbulence for low-mass cores.

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Section: Summary and Discussionmentioning

confidence: 99%

Pebble Accretion in Turbulent Protoplanetary Disks

Bai

Murray-Clay

2017

ApJ

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“…Such an onion-shell structure would have less H 2 dissolved in the magma, and (for a nebula volatile source) less H 2 O in the atmosphere, than for our default model. Finally, the magma ocean might form volatilepoor if silicate cores reach full size in an environment that has a low base-of-atmosphere pressure (e.g., Ormel et al 2015). In this last case, convection is needed for non-negligible equilibration (Pahlevan et al 2019).…”

Section: How Long For Magma-atmosphere Equilibration?mentioning

confidence: 99%

Atmosphere Origins for Exoplanet Sub-Neptunes

Kite

Fegley

Schaefer

et al. 2020

ApJ

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Planets with 2 R ⊕ < R < 3 R ⊕ and orbital period <100 d are abundant; these sub-Neptune exoplanets are not well understood. For example, Kepler sub-Neptunes are likely to have deep magma oceans in contact with their atmospheres, but little is known about the effect of the magma on the atmosphere. Here we study this effect using a basic model, assuming that volatiles equilibrate with magma at T ∼ 3000 K. For our Fe-Mg-Si-O-H model system, we find that chemical reactions between the magma and the atmosphere and dissolution of volatiles into the magma are both important. Thus, magma matters. For H, most moles go into the magma, so the mass target for both H 2 accretion and H 2 loss models is weightier than is usually assumed. The known span of magma oxidation states can produce sub-Neptunes that have identical radius but with total volatile masses varying by 20-fold. Thus, planet radius is a proxy for atmospheric composition but not for total volatile content. This redox diversity degeneracy can be broken by measurements of atmosphere mean molecular weight. We emphasise H 2 supply by nebula gas, but also consider solid-derived H 2 O. We find that adding H 2 O to Fe probably cannot make enough H 2 to explain sub-Neptune radii because >10 3 -km thick outgassed atmospheres have high mean molecular weight. The hypothesis of magma-atmosphere equilibration links observables such as atmosphere H 2 O/H 2 ratio to magma FeO content and planet formation processes. Our model's accuracy is limited by the lack of experiments (lab and/or numerical) that are specific to sub-Neptunes; we advocate for such experiments.

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“…In this study, we assume that a disk gas freely flows into a planet until atmospheric contraction due to radiative cooling occurs. Recently, Ormel et al (2015) found that a rapid recycle of the atmospheric gas suppresses gas accretion onto a planet embedded in an isothermal disk, whereas Kurokawa & Tanigawa (2018) showed that the atmospheric recycling of a planet should be less efficient in non-isothermal cases because of the buoyancy barrier. In addition, small grains may be suspended in an accreting H 2 -rich gas flow, leading to the delay of atmospheric cooling (Lambrechts & Lega 2017).…”

Section: Gas Accretion Onto a Planetmentioning

confidence: 99%

Do the TRAPPIST-1 Planets Have Hydrogen-rich Atmospheres?

Hori

Ogihara

2020

ApJ

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Recently, transmission spectroscopy in the atmospheres of the TRAPPIST-1 planets revealed flat and featureless absorption spectra, which rule out cloud-free, hydrogen-dominated atmospheres. Earthsized planets orbiting TRAPPIST-1 likely have either a clear or a cloudy/hazy, hydrogen-poor atmosphere. In this paper, we investigate whether a proposed formation scenario is consistent with expected atmospheric compositions of the TRAPPIST-1 planets. We examine the amount of a hydrogen-rich gas that TRAPPIST-1-like planets accreted from the ambient disk until disk dispersal. Since TRAPPIST-1 planets are trapped into a resonant chain, we simulate disk gas accretion onto a migrating TRAPPIST-1-like planet. We find that the amount of an accreted hydrogen-rich gas is as small as 10 −2 wt% and 0.1 wt% for TRAPPIST-1 b and 1 c, 10 −2 wt% for 1 d, 1 wt% for 1 e, a few wt% for 1 f and 1 g and 1 wt% for 1 h, respectively. We also calculate the long-term thermal evolution of TRAPPIST-1-like planets after disk dissipation and estimate the mass loss of their hydrogen-rich atmospheres driven by a stellar X-ray and UV irradiation. We find that all the accreted hydrogen-rich atmospheres can be lost via hydrodynamic escape. Therefore, we conclude that TRAPPIST-1 planets should have no primordial hydrogen-rich gases but secondary atmospheres such as a Venus-like one and water vapor, if they currently retain atmospheres.

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Hydrodynamics of embedded planets’ first atmospheres – II. A rapid recycling of atmospheric gas

Cited by 188 publications

References 42 publications

Pebble Accretion in Turbulent Protoplanetary Disks

Pebble Accretion in Turbulent Protoplanetary Disks

Atmosphere Origins for Exoplanet Sub-Neptunes

Do the TRAPPIST-1 Planets Have Hydrogen-rich Atmospheres?

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