Free energy models for ice VII and liquid water derived from pressure, entropy, and heat capacity relations

Myint, Philip C.; Benedict, Lorin X.; Belof, Jonathan L.

doi:10.1063/1.4989582

Cited by 26 publications

(24 citation statements)

References 64 publications

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“…We assumed c p,f ∼ 3800 J kg −1 K −1 . The approximation of c p,f as constant is justified by Myint et al (2017). We extrapolated the tables above 6 GPa, and for T < 80 • C. Clathrates were neglected.…”

Section: Cycle-dependent Versus Cycle-independent Planetary Habitabilitymentioning

confidence: 99%

Habitability of Exoplanet Waterworlds

Kite

Ford

2018

ApJ

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Many habitable zone (HZ) exoplanets are expected to form with water mass fractions higher than that of the Earth. For rocky exoplanets with 10-1000× Earth's H 2 O but without H 2 , we model the multi-Gyr evolution of ocean temperature and chemistry, taking into account C partitioning, high-pressure ice phases, and atmosphere-lithosphere exchange. Within our model, for Sun-like stars, we find that:(1) the duration of habitable surface water is strongly affected by ocean chemistry; (2) possible ocean pH spans a wide range; (3) surprisingly, many waterworlds retain habitable surface water for >1 Gyr, and (contrary to previous claims) this longevity does not necessarily involve geochemical cycling.The key to this cycle-independent planetary habitability is that C exchange between the convecting mantle and the water ocean is curtailed by seafloor pressure on waterworlds, so the planet is stuck with the ocean mass and ocean cations that it acquires during the first 1% of its history. In our model, the sum of positive charges leached from the planetary crust by early water-rock interactions is -coincidentally -often within an order of magnitude of the early-acquired atmosphere+ocean inorganic C inventory overlaps. As a result, p CO2 is frequently in the "sweet spot" (0.2-20 bar) for which the range of semimajor axis that permits surface liquid water is about as wide as it can be. Because the width of the HZ in semimajor axis defines (for Sun-like stars) the maximum possible time span of surface habitability, this effect allows for Gyr of habitability as the star brightens. We illustrate our findings by using the output of an ensemble of N -body simulations as input to our waterworld evolution code. Thus (for the first time in an end-to-end calculation) we show that chance variation of initial conditions, with no need for geochemical cycling, can yield multi-Gyr surface habitability on waterworlds.

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Section: Cycle-dependent Versus Cycle-independent Planetary Habitabilitymentioning

confidence: 99%

Habitability of Exoplanet Waterworlds

Kite

Ford

2018

ApJ

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“…Ice VII has a body-centered cubic (BCC) lattice of oxygen. All the curves in the phase diagram are produced from our equation of state (EOS) for the two water phases [15]. Unlike single-shock compression (where the relevant curve is the Hugoniot), quasi-isentropic compression can probe deeply undercooled states since the temperature rise along its loading path is far more attenuated.…”

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confidence: 99%

Nanosecond Freezing of Water at High Pressures: Nucleation and Growth near the Metastability Limit

et al. 2018

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The fundamental study of phase transition kinetics has motivated experimental methods toward achieving the largest degree of undercooling possible, more recently culminating in the technique of rapid, quasi-isentropic compression. This approach has been demonstrated to freeze water into the high-pressure ice VII phase on nanosecond time scales, with some experiments undergoing heterogeneous nucleation while others, in apparent contradiction, suggesting a homogeneous nucleation mode. In this study, we show through a combination of theory, simulation, and analysis of experiments that these seemingly contradictory results are in agreement when viewed from the perspective of classical nucleation theory. We find that, perhaps surprisingly, classical nucleation theory is capable of accurately predicting the solidification kinetics of ice VII formation under an extremely high driving force (|∆µ/k B T | ≈ 1), but only if amended by two important considerations: 1) transient nucleation and 2) separate liquid and solid temperatures. This is the first demonstration of a model that is able to reproduce the experimentally observed rapid freezing kinetics.

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“…The second feature of the temperature-density graph is the density discontinuity between the fluid state and the solid state along the melting curve, most prominently between Ice VII and fluid, which typically amounts to the order of a few percent (Goncharov et al 2009;Bezacier et al 2014;Myint et al 2017).…”

Section: Perspective From Visualized Water Equations Of Statementioning

confidence: 99%

New Perspectives on the Exoplanet Radius Gap from a Mathematica Tool and Visualized Water Equation of State

Zeng

Jacobsen

Hyung

et al. 2021

ApJ

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Recent astronomical observations obtained with the Kepler and TESS missions and their related ground-based follow-ups revealed an abundance of exoplanets with a size intermediate between Earth and Neptune (1 R ⊕ ≤ R ≤ 4 R ⊕). A low occurrence rate of planets has been identified at around twice the size of Earth (2 × R ⊕), known as the exoplanet radius gap or radius valley. We explore the geometry of this gap in the mass–radius diagram, with the help of a Mathematica plotting tool developed with the capability of manipulating exoplanet data in multidimensional parameter space, and with the help of visualized water equations of state in the temperature–density (T–ρ) graph and the entropy–pressure (s–P) graph. We show that the radius valley can be explained by a compositional difference between smaller, predominantly rocky planets (<2 × R ⊕) and larger planets (>2 × R ⊕) that exhibit greater compositional diversity including cosmic ices (water, ammonia, methane, etc.) and gaseous envelopes. In particular, among the larger planets (>2 × R ⊕), when viewed from the perspective of planet equilibrium temperature (T eq), the hot ones (T eq ≳ 900 K) are consistent with ice-dominated composition without significant gaseous envelopes, while the cold ones (T eq ≲ 900 K) have more diverse compositions, including various amounts of gaseous envelopes.

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Free energy models for ice VII and liquid water derived from pressure, entropy, and heat capacity relations

Cited by 26 publications

References 64 publications

Habitability of Exoplanet Waterworlds

Habitability of Exoplanet Waterworlds

Nanosecond Freezing of Water at High Pressures: Nucleation and Growth near the Metastability Limit

New Perspectives on the Exoplanet Radius Gap from a Mathematica Tool and Visualized Water Equation of State

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