Chemical processes in the deep interior of Uranus

Chau, R.; Hamel, Sébastien; Nellis, W. J.

doi:10.1038/ncomms1198

Cited by 86 publications

(85 citation statements)

References 29 publications

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“…Molecules with short-lived (< 15 fs) C C bonds were observed in these simulations. These results show a similar be havior to CH 4 [31] and a bulk C:H:O:N liquid [32] which also developed molecules with short-lived C C bonds at high temperatures. Our results suggest that complete dissociation of CO has not occurred at 9000 K and low pressures.…”

Section: Co Dissociationsupporting

confidence: 61%

“…Numerical models of magnetic field generation field on Uranus and Neptune compared with observational information about their magnetic favor dynamo generation in a layer of convecting liquid characterized by poor conductivity [10][11][12]. Recent findings show that the development of C C bonds in H O C N liquids greatly affects their conductivity and viscosity, which in turn impacts the magnetic Reynolds number and the nature of a magnetic field generated by the liquid [32]. The development of C C in our simulations potentially correlates to changes in CO properties.…”

Section: Melting Line and Implications For Giant Planet Interiorsmentioning

confidence: 99%

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Ab initio simulations of liquid carbon monoxide at high pressure

Leonhardi

Militzer

2017

High Energy Density Physics

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A B S T R A C TCarbon monoxide occurs as a volatile species in the interiors of terrestrial planets, and as a disequilibrium atmospheric constituent in the giant planets. It plays an important role during the accretionary stages of planet formation reacting with gases to form compounds such as CH 4 and H 2 O. The structure of carbon monoxide is unknown over the majority of the temperature and pressure regime in giant planet interiors. Here we perform ab initio molecular dynamics simulations to characterize CO to 140 GPa and 5,000 K. We find that CO is stable as a molecular liquid at lower P-T conditions, as a polymeric liquid at higher P-T conditions found in ice giant interiors, and as a plasma at high-T.

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Section: Co Dissociationsupporting

confidence: 61%

Section: Melting Line and Implications For Giant Planet Interiorsmentioning

confidence: 99%

Ab initio simulations of liquid carbon monoxide at high pressure

Leonhardi

Militzer

2017

High Energy Density Physics

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“…These planets are postulated to have mantles consisting of mixture of fluid methane, water and ammonia, where these compounds have a role similar to that of minerals in the Earth's mantle 1 . The effects of possible formation of mixtures between methane, water and ammonia 30,31 and ionization 3 were shown to occur at higher temperatures than those studied in this work. Notwithstanding this, our study offers evidence for chemical reactivity of C-H component of planetary ices, which may also affect positions of planetary isentropes.…”

Section: Discussionmentioning

confidence: 60%

Carbon precipitation from heavy hydrocarbon fluid in deep planetary interiors

Lobanov

Chen

et al. 2013

Nat Commun

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The phase diagram of the carbon-hydrogen system is of great importance to planetary sciences, as hydrocarbons comprise a significant part of icy giant planets and are involved in reduced carbon-oxygen-hydrogen fluid in the deep Earth. Here we use resistively-and laser-heated diamond anvil cells to measure methane melting and chemical reactivity up to 80 GPa and 2,000 K. We show that methane melts congruently below 40 GPa. Hydrogen and elementary carbon appear at temperatures of 41,200 K, whereas heavier alkanes and unsaturated hydrocarbons (424 GPa) form in melts of 41,500 K. The phase composition of carbon-hydrogen fluid evolves towards heavy hydrocarbons at pressures and temperatures representative of Earth's lower mantle. We argue that reduced mantle fluids precipitate diamond upon re-equilibration to lighter species in the upwelling mantle. Likewise, our findings suggest that geophysical models of Uranus and Neptune require reassessment because chemical reactivity of planetary ices is underestimated.

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“…At high pressure, condensation of the freed carbon atoms may ensue. It is of particular interest to compare our model, which we confine to the molecular solid regime, with the phase diagram for synthetic Uranus, derived experimentally by Chau et al (2011). The introduction of carbon atoms to a water surrounding, at a pressure above 100 GPa and a temperature beyond 1000 K, introduces a super-ionic phase whose extent of stability is narrower than the corresponding phase for a pure water system.…”

Section: The Mantle Thermal Profilementioning

confidence: 99%

“…At even higher temperatures (2000-4000 K), depending on pressure, a reticulating phase is introduced, where methane dissociates, releasing excess hydrogen. The relatively long lifetime of the C-C bond results in the formation of dense carbon clusters that should tend to segregate and sink (Chau et al 2011).…”

Section: The Mantle Thermal Profilementioning

confidence: 99%

STRUCTURE AND DYNAMICS OF COLD WATER SUPER-EARTHS: THE CASE OF OCCLUDED CH₄AND ITS OUTGASSING

Levi

Sasselov

Podolak

2014

ApJ

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In this work, we study the transport of methane in the external water envelopes surrounding water-rich super-Earths. We investigate the influence of methane on the thermodynamics and mechanics of the water mantle. We find that including methane in the water matrix introduces a new phase (filled ice), resulting in hotter planetary interiors. This effect renders the super-ionic and reticulating phases accessible to the lower ice mantle of relatively low-mass planets (∼5 M E ) lacking a H/He atmosphere. We model the thermal and structural profile of the planetary crust and discuss five possible crustal regimes which depend on the surface temperature and heat flux. We demonstrate that the planetary crust can be conductive throughout or partly confined to the dissociation curve of methane clathrate hydrate. The formation of methane clathrate in the subsurface is shown to inhibit the formation of a subterranean ocean. This effect results in increased stresses on the lithosphere, making modes of ice plate tectonics possible. The dynamic character of the tectonic plates is analyzed and the ability of this tectonic mode to cool the planet is estimated. The icy tectonic plates are found to be faster than those on a silicate super-Earth. A mid-layer of low viscosity is found to exist between the lithosphere and the lower mantle. Its existence results in a large difference between ice mantle overturn timescales and resurfacing timescales. Resurfacing timescales are found to be 1 Ma for fast plates and 100 Ma for sluggish plates, depending on the viscosity profile and ice mass fraction. Melting beneath spreading centers is required in order to account for the planetary radiogenic heating. The melt fraction is quantified for the various tectonic solutions explored, ranging from a few percent for the fast and thin plates to total melting of the upwelled material for the thick and sluggish plates. Ice mantle dynamics is found to be important for assessing the composition of the atmosphere. We propose a mechanism for methane release into the atmosphere, where freshly exposed reservoirs of methane clathrate hydrate at the ridge dissociate under surface conditions. We formulate the relation between the outgassing flux and the tectonic mode dynamical characteristics. We give numerical estimates for the global outgassing rate of methane into the atmosphere. We find, for example, that for a 2 M E planet outgassing can release 10 27 -10 29 molecules s −1 of methane to the atmosphere. We suggest a qualitative explanation for how the same outgassing mechanism may result in either a stable or a runaway volatile release, depending on the specifics of a given planet. Finally, we integrate the global outgassing rate for a few cases and quantify how the surface atmospheric pressure of methane evolves over time. We find that methane is likely an important constituent of water planets' atmospheres.

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Chemical processes in the deep interior of Uranus

Cited by 86 publications

References 29 publications

Ab initio simulations of liquid carbon monoxide at high pressure

Ab initio simulations of liquid carbon monoxide at high pressure

Carbon precipitation from heavy hydrocarbon fluid in deep planetary interiors

STRUCTURE AND DYNAMICS OF COLD WATER SUPER-EARTHS: THE CASE OF OCCLUDED CH₄AND ITS OUTGASSING

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Chemical processes in the deep interior of Uranus

Cited by 86 publications

References 29 publications

Ab initio simulations of liquid carbon monoxide at high pressure

Ab initio simulations of liquid carbon monoxide at high pressure

Carbon precipitation from heavy hydrocarbon fluid in deep planetary interiors

STRUCTURE AND DYNAMICS OF COLD WATER SUPER-EARTHS: THE CASE OF OCCLUDED CH4AND ITS OUTGASSING

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STRUCTURE AND DYNAMICS OF COLD WATER SUPER-EARTHS: THE CASE OF OCCLUDED CH₄AND ITS OUTGASSING