The opacity of grains in protoplanetary atmospheres

Movshovitz, N.; Podolak, M.

doi:10.1016/j.icarus.2007.09.018

Cited by 82 publications

(121 citation statements)

References 14 publications

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“…In contrast, outside 4.5×10 11 cm, the opacity increases with f D/G,disk (variation by a factor of ∼20). This is again a clear sign that in the outermost layers, Brownian coagulation is important (Movshovitz & Podolak 2008).…”

Section: Impact Of the Dust-to-gas Ratio In The Diskmentioning

confidence: 83%

“…By construction, in all three regimes, the growth and settling timescales are the same. Movshovitz & Podolak (2008) found that the grain evolution approaches a steady state in only 100 yrs, and that after 1000 yrs, the steady state is fully established. Similarly short timescales are also found in the analytical model.…”

Section: Timescalesmentioning

confidence: 99%

“…It is clear that a sticking efficiency of less than unity would also affect the timescales. Movshovitz & Podolak (2008) investigated the effect of uniformly reduced sticking efficiencies. At a lower efficiency of 0.4, the opacity increased mildly.…”

Section: Settling Velocity Dust Density and Extinction Efficiencymentioning

confidence: 99%

“…6 shows the mass density of dust (ρ × f D/G ) as a function of height. Movshovitz & Podolak (2008) show the same quantity in their Fig. 5, and their curve is also included here.…”

Section: Settling Velocity Dust Density and Extinction Efficiencymentioning

confidence: 99%

“…(35), (41)). Movshovitz & Podolak (2008) investigated the impact of varying f D/G,disk between 0.001 and 0.02, i.e., by a factor of 20. For Brownian coagulation, this would lead to a variation of κ gr by a factor of approximately five according to the analytical estimates.…”

Section: Impact Of the Dust-to-gas Ratio In The Diskmentioning

confidence: 99%

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Grain opacity and the bulk composition of extrasolar planets

Mordasini

2014

A&A

100

114

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Context. We investigate the grain opacity κ gr in the atmosphere (outer radiative zone) of forming planets. This is important for the observed planetary mass-radius relationship since κ gr affects the primordial H/He envelope mass of low-mass planets and the critical core mass of giant planets. Aims. The goal of this study is to derive a simple analytical model for κ gr and to explore its implications for the atmospheric structure and resulting gas accretion rate. Methods. Our model is based on the comparison of the timescales of the most important microphysical processes. We consider grain settling in the Stokes and Epstein drag regime, growth by Brownian motion coagulation and differential settling, grain evaporation in hot layers, and grain advection due to the contraction of the envelope. With these timescales and the assumption of a radially constant grain flux, we derive the typical grain size, abundance, and opacity. Results. We find that the dominating growth process is differential settling. In this regime, κ gr has a simple functional form; it is given as 27Q/8Hρ in the Epstein regime in the outer atmosphere and as 2Q/Hρ for Stokes drag in the deeper layers. Grain growth leads to a typical radial structure of κ gr with high ISM-like values in the outer layers but a strong decrease towards the deeper parts where κ gr becomes so low that the grain-free molecular opacities take over. Conclusions. In agreement with earlier results, we find that κ gr is typically much lower than in the ISM. In retrospect, this suggests that classical giant planet formation models should have considered the grain-free case to be as equally meaningful as the full ISM opacity case. The equations also show that a higher dust input in the top layers does not strongly increase κ gr . This has two important implications. First, for the formation of giant planet cores via pebbles, there could be the adverse effect that pebbles tend to increase the grain input high in the atmosphere because of ablation. This could in principle increase the opacity, making giant planet formation difficult. Our study indicates that this potentially adverse effect is not important. Second, it means that a higher stellar [Fe/H] which presumably leads to a higher surface density of planetesimals only favors giant planet formation without being detrimental to it because of an increased κ gr . This corroborates the result that core accretion can explain the observed increase of the giant planet frequency with stellar [Fe/H].

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Section: Impact Of the Dust-to-gas Ratio In The Diskmentioning

confidence: 83%

Section: Timescalesmentioning

confidence: 99%

Section: Settling Velocity Dust Density and Extinction Efficiencymentioning

confidence: 99%

“…6 shows the mass density of dust (ρ × f D/G ) as a function of height. Movshovitz & Podolak (2008) show the same quantity in their Fig. 5, and their curve is also included here.…”

Section: Settling Velocity Dust Density and Extinction Efficiencymentioning

confidence: 99%

Section: Impact Of the Dust-to-gas Ratio In The Diskmentioning

confidence: 99%

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Grain opacity and the bulk composition of extrasolar planets

Mordasini

2014

A&A

100

114

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Core‐Accretion Model

Hubickyj

2010

Formation and Evolution of Exoplanets

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IntroductionFifteen years ago planetary formation models were constrained by the observational data of the planets in the solar system. Since the discovery of the companion orbiting 51 Peg [1, 2], planetary formation models need to explain the planets in the solar system and the over 300 confirmed-observed exoplanets and over 30 candidates of multiple planet systems around stars other than the Sun. We have found that these exoplanets are diverse in their characteristics. The mission of searching for Earth-sized planets, Kepler, will increase the number and diversity of planets and pose new challenges to planetary formation models.The goal of this chapter is to review the core-accretion gas capture ((CAGC) or core accretion) model for the formation of the gas giant planets. In this model, planetesimals accrete into a solid core that eventually gravitationally accretes gas from the solar nebula. This chapter provides the basic information that an interested reader would need to acquire a robust understanding of the model in its theoretical and computational form.Section 5.2 contains a brief historical review of the progenitors of this model and the results of and the progress made by these early investigators. Section 5.3 describes the observational constraints on this proposed model. Section 5.4 provides an overview of the core-accretion model describing the protoplanet's growth from an embryo to a gas giant planet. Section 5.5 introduces the mathematical structure of the model, the boundary conditions, and the assumptions applied in the simulation. Section 5.6 discusses the results of the simulations, focusing on the description of the work by the NASA/ARC and UCSC group. Section 5.7 presents a discussion of topics related to the core-accretion model and final remarks. Historical Background of the Development of the Core Accretion ModelSince the time planets were distinguished from stars, people have thought about their origin. Descartes [3], Kant [4], Laplace [5], and Herschel [6] formalized the Formation and Evolution of Exoplanets. Edited by Rory Barnes

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