Dissociation of MgSiO
            <sub>3</sub>
            in the Cores of Gas Giants and Terrestrial Exoplanets

Umemoto, Koichiro; Wentzcovitch, Renata M.; Allen, Philip B.

doi:10.1126/science.1120865

Cited by 179 publications

(171 citation statements)

References 21 publications

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“…For the silicate melting point, we assume the Lindemann melting law [58] 8) wherem andv are the mean atomic mass and volume, respectively, k B is the Boltzmann constant, h is the Planck constant divided by 2π , θ is the Debye temperature and f is the critical ratio of vibration amplitude to atomic spacing at melting. For applications to the core-mantle boundary of super-earths, we assume that the solid phase is MgSiO 3 post-perovskite [59,60], and compute the volume and Debye temperature as a function of pressure along the 1600 K adiabat from the thermodynamic model of [38]. We chose the value of f = 0.…”

Section: −2β Pmentioning

confidence: 99%

Melting in super-earths

Stixrude

2014

Phil. Trans. R. Soc. A.

104

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We examine the possible extent of melting in rockiron super-earths, focusing on those in the habitable zone. We consider the energetics of accretion and core formation, the timescale of cooling and its dependence on viscosity and partial melting, thermal regulation via the temperature dependence of viscosity, and the melting curves of rock and iron components at the ultra-high pressures characteristic of superearths. We find that the efficiency of kinetic energy deposition during accretion increases with planetary mass; considering the likely role of giant impacts and core formation, we find that super-earths probably complete their accretionary phase in an entirely molten state. Considerations of thermal regulation lead us to propose model temperature profiles of super-earths that are controlled by silicate melting. We estimate melting curves of iron and rock components up to the extreme pressures characteristic of superearth interiors based on existing experimental and ab initio results and scaling laws. We construct superearth thermal models by solving the equations of mass conservation and hydrostatic equilibrium, together with equations of state of rock and iron components. We set the potential temperature at the core-mantle boundary and at the surface to the local silicate melting temperature. We find that ancient (∼4 Gyr) super-earths may be partially molten at the top and bottom of their mantles, and that mantle convection is sufficiently vigorous to sustain dynamo action over the whole range of super-earth masses.

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Section: −2β Pmentioning

confidence: 99%

Melting in super-earths

Stixrude

2014

Phil. Trans. R. Soc. A.

104

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“…According to Umemoto et al [2006a] a large decrease in enthalpy at the pyrite-type → cotunnite-type transition in SiO 2 stabilizes the breakdown products with respect to MgSiO 3 , due mainly to the higher density of the cotunnite-type SiO 2 + B2-MgO than MgSiO 3 -PPv. NaMgF 3 is a good analog material for MgSiO 3 because its breakdown occurs from the same thermodynamic driving force [Umemoto et al, 2006b].…”

Section: Introductionmentioning

confidence: 99%

“…[3] Recent first-principles calculations by Umemoto et al [2006a] proposed that the post-perovskite form of MgSiO 3 breaks down to an oxide mixture (MgO + SiO 2 ) at ∼1000 GPa, corresponding to the core-mantle boundary pressure in 10M È super-Earths. They predicted a strongly negative Clapeyron slope (dP/dT = −30 MPa/K) of the breakdown -at least an order of magnitude larger than the post-spinel transition.…”

Section: Introductionmentioning

confidence: 99%

Stability of the MgSiO₃ analog NaMgF₃ and its implication for mantle structure in super‐Earths

Grocholski

Shim

Prakapenka

2010

Geophysical Research Letters

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First‐principles calculations on MgSiO3 suggested a breakdown into MgO + SiO2 at pressure above 1000 GPa with an extremely large negative Clapeyron slope, isolating the lowermost mantles of larger super‐Earths (∼10M⊕) from convection. Similar calculations predicted the same type of breakdown in NaMgF3 to NaF + MgF2 at 40 GPa, allowing for experimental examination. We found that NaMgF3 is stable to at least 70 GPa and 2500 K. In our measurements on MgF2 (an SiO2 analog), we found a previously unidentified phase (“phase X”) between the stability fields of pyrite‐type and cotunnite‐type (49–53 GPa and 1500–2500 K). A very small density increase (1%) at the pyrite‐type → phase X transition would extend the stability of NaMgF3 relative to the breakdown products. Furthermore, because phase X appears to have a cation coordination number intermediate between pyrite‐type (6) and cotunnite‐type (9), entropy change (ΔS) would be smaller at the breakdown boundary, making the Clapeyron slope (dP/dT = ΔS/ΔV) much smaller than the prediction. If similar trend occurs in MgSiO3 and SiO2, the breakdown of MgSiO3 may occur at higher pressure and have much smaller negative Clapeyron slope than the prediction, allowing for large‐scale convection in the mantles of super‐Earth exoplanets.

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“…For example the very existence of planetary cores, their masses, as well as the amount and distribution of heavy elements in the planets' core or in their envelopes, remain undetermined. Recently, Wilson & Militzer (2012) suggested that planetary cores, mostly composed of rock and ices, can be eroded and/or dissolve (depending on their mass) into the metallic H/He layers above, and thus be redistributed in the planetary envelope (see also Umemoto et al 2006). This can have significant implications for giant planets' thermal evolution, their radius contraction, and overall structure.…”

Section: Wasp-56b and Wasp-57bmentioning

confidence: 99%

WASP-54b, WASP-56b, and WASP-57b: Three new sub-Jupiter mass planets from SuperWASP

Faedi

Pollacco

Barros

et al. 2013

A&A

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We present three newly discovered sub-Jupiter mass planets from the SuperWASP survey: WASP-54b is a heavily bloated planet of mass 0.636 +0.025 −0.024 M J and radius 1.653 +0.090 −0.083 R J . It orbits a F9 star, evolving off the main sequence, every 3.69 days. Our MCMC fit of the system yields a slightly eccentric orbit (e = 0.067 +0.033 −0.025 ) for WASP-54b. We investigated further the veracity of our detection of the eccentric orbit for WASP-54b, and we find that it could be real. However, given the brightness of WASP-54 V = 10.42 mag, we encourage observations of a secondary eclipse to draw robust conclusions on both the orbital eccentricity and the thermal structure of the planet. WASP-56b and WASP-57b have masses of 0.571 +0.034 −0.035 M J and 0.672 +0.049 −0.046 M J , respectively; and radii of 1.092 +0.035 −0.033 R J for WASP-56b and 0.916 +0.017 −0.014 R J for WASP-57b. They orbit main sequence stars of spectral type G6 every 4.67 and 2.84 days, respectively. WASP-56b and WASP-57b show no radius anomaly and a high density possibly implying a large core of heavy elements; possibly as high as ∼50 M ⊕ in the case of WASP-57b. However, the composition of the deep interior of exoplanets remains still undetermined. Thus, more exoplanet discoveries such as the ones presented in this paper, are needed to understand and constrain giant planets' physical properties.

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Dissociation of MgSiO ₃ in the Cores of Gas Giants and Terrestrial Exoplanets

Cited by 179 publications

References 21 publications

Melting in super-earths

Melting in super-earths

Stability of the MgSiO₃ analog NaMgF₃ and its implication for mantle structure in super‐Earths

WASP-54b, WASP-56b, and WASP-57b: Three new sub-Jupiter mass planets from SuperWASP

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Dissociation of MgSiO 3 in the Cores of Gas Giants and Terrestrial Exoplanets

Cited by 179 publications

References 21 publications

Melting in super-earths

Melting in super-earths

Stability of the MgSiO3 analog NaMgF3 and its implication for mantle structure in super‐Earths

WASP-54b, WASP-56b, and WASP-57b: Three new sub-Jupiter mass planets from SuperWASP

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Dissociation of MgSiO ₃ in the Cores of Gas Giants and Terrestrial Exoplanets

Stability of the MgSiO₃ analog NaMgF₃ and its implication for mantle structure in super‐Earths