AQUA: A Collection of H 2 O Equations of State for Planetary Models
Jonas Haldemann, Yann Alibert, Christoph Mordasini, Willy Benz
AAstronomy & Astrophysics manuscript no. waterpaper c (cid:13)
ESO 2020September 23, 2020
AQUA: A Collection of H O Equations of State for PlanetaryModels (cid:63)
Jonas Haldemann , Yann Alibert , Christoph Mordasini , and Willy Benz Department of Space Research & Planetary Sciences, University of Bern, Gesellschaftsstrasse 6, 3012 Bern, SwitzerlandReceived 07 Mai 2020 / Accepted 18 September 2020
ABSTRACT
Context.
Water is one of the key chemical elements in planetary structure modelling. Due to its complex phase diagram, equations ofstate cover often only parts of the pressure – temperature space needed in planetary modelling.
Aims.
We construct an equation of state of H O spanning a very wide range from 0 . K, which canbe used to model the interior of planets.
Methods.
We combine equations of state valid in localised regions to form a continuous equation of state spanning over said pressureand temperature range.
Results.
We provide tabulated values for the most important thermodynamic quantities, i.e., density, adiabatic temperature gradient,entropy, internal energy and bulk speed of sound of water over this pressure and temperature range. For better usability we alsocalculated density – temperature and density – internal energy grids. We discuss further the impact of this equation of state on themass radius relation of planets compared to other popular equation of states like ANEOS and QEOS.
Conclusions.
AQUA is a combination of existing equation of state useful for planetary models. We show that AQUA is in mostregions a thermodynamic consistent description of water. At pressures above 10 GPa AQUA predicts systematic larger densities thanANEOS or QEOS. A feature which was already present in a previously proposed equation of state, which is the main underlyingequation of this work. We show that the choice of the equation of state can have a large impact on the mass-radius relation, whichhighlights the importance of future developments in the field of equation of states and regarding experimental data of water at highpressures.
Key words.
Equation of state – Planets and satellites: interiors – Methods: numerical
1. Introduction
Due to its abundance in the universe and its chemical proper-ties, water is the key component in planetary models. It plays amajor role during the formation and evolution of planets and atthe same time it is thought to be a key ingredient in the emer-gence of life on Earth (Allen et al. 2003; Wiggins 2008). Wefind water not only in Earths hydrosphere but throughout the so-lar system, in the gas- & ice-giants, their moons, in comets andother minor bodies (Grasset et al. 2017). Water is besides H / Healso thought to be a dominant component in the atmospheresof giant exoplanets (van Dishoeck et al. 2014) while on smallerexoplanets it might form large oceans or thick ice-sheets (Sotinet al. 2007). The environments where water is expected to occurdi ff er largely in their pressure and temperature conditions. Toaccurately model the interior structure of planets, a consistentdescription of the thermodynamic properties of water is neededover large pressure and temperature scales. Especially in an-ticipation of improved planetary radius measurements by spacemissions like CHEOPS (Benz et al. 2017) or PLATO (Rauer &Heras 2018), which require an accurate description of the planetmajor constituents, in order to constrain the planets bulk compo-sition. In this work we combine multiple equations of state (EoS) Send o ff print requests to : Jonas Haldemann, e-mail: [email protected] (cid:63) Tables B.6, B.7 and B.8 are only available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/ all covering some part of the pressure and temperature (P – T)space of water to construct an EoS useful for planetary structuremodelling.The phase diagram of water is highly diverse, including mul-tiple ice phases and triple points. At ambient conditions the ther-modynamic properties of water are well studied. The canonicalreference, for pressures up to 1 GPa and temperatures of 1273K, is provided by the International Association for the Proper-ties of Water and Steam (IAPWS) in their IAPWS-R6-95 release(Wagner & Pruß 2002) and for ice-1h in the IAPWS-R10-06 re-lease (Feistel & Wagner 2006). Recently Bollengier et al. (2019);Brown (2018) expanded the validity region of their liquid-waterEoS to higher pressures (2.3 GPa, respectively 100 GPa). At evenhigher pressures experimental data is more sparse and most workrely on ab initio calculations to construct EoS.Recently Mazevet et al. (2019) published an ab initio equa-tion of state which spans over a pressure and temperature rangeuseful for modelling the interior of giant planets. However due tothe complications of low density ab initio calculations the EoSis less accurate in low density regions ( (cid:46) / cm ) of the P–Tspace . It also does not include any ice phases which are an im-portant factor in models where the water is close or at the surfaceof planets. In this paper we show how one can combine the EoSof Mazevet et al. (2019) with other EoS which are more suit-able at lower pressures and densities namely French & Redmer Although the results of Wagner & Pruß (2002) are used by Mazevetet al. (2019) to improve the provided fit towards lower temperatures.Article number, page 1 of 20 a r X i v : . [ a s t r o - ph . E P ] S e p & A proofs: manuscript no. waterpaper (2015); Journaux et al. (2020); Feistel & Wagner (2006); Wag-ner & Pruß (2002); Gordon (1994). The resulting EoS can thenbe used to not only model water at high pressures and temper-atures in planetary interiors as in Mazevet et al. (2019) but alsoto model planetary atmospheres, surfaces or moons, where waterappears at lower temperatures and pressures.We would like to note that we do not attempt to provide abetter or novel EoS of water for the regions where the individualEoS were constructed for. The goal is rather to provide a con-tinuous formulation of thermodynamic properties of water overlarge pressure and temperature scales. This is a crucial point inorder to numerically solve the interior structure equations oftenused in planetary modelling.This paper is structured in the following way. In section 2 wedescribe the used EoS in more detail. We show where each EoSis used and how we transition between them. In section 3 wecalculate the thermodynamic consistency of our approach andcompare the resulting EoS with other EoS for water. In section4 we use the AQUA-EoS to calculate mass radius relations forvarious boundary conditions and compare it against other com-mon EoS. In the last section 5 we discuss the major findingsof this work. A public available version of the EoS in tabulatedform (available as P-T, ρ -T and ρ -u grids.) can be found onlineat https://github.com/mnijh/AQUA .
2. Methods
In the following section we describe how we combined the EoSof Mazevet et al. (2019) (hereafter M19-EoS) with other EoSwhich complement the M19-EoS at lower pressures and temper-atures. All in perspective of developing a description of ther-modynamic quantities used to model the interiors of planetsand their satellites. The quantities we focus on are the density ρ ( T , P ), the specific entropy s ( T , P ), the specific internal energy u ( T , P ), the bulk speed of sound w ( T , P ) = (cid:115)(cid:32) ∂ P ∂ρ (cid:33) S (1)and the adiabatic temperature gradient defined as ∇ Ad = (cid:32) ∂ ln T ∂ ln P (cid:33) S = α v Tc P ρ PT , (2)where α v is the volumetric thermal expansion coe ffi cient and c P is the specific isobaric heat capacity. These quantities canbe calculated from first or second order derivatives of a Gibbsor Helmholtz free energy potential. Finding a single functionalform which accurately describes one of these energy potentialsover the large phase space needed is very challenging and wasnot yet accomplished. Though there are many EoS describingthe properties of H O in a localised region. We propose to use aselection of such local descriptions to construct an EoS of H Ospanning from 0 . K. A similar method, though fora smaller P-T range and di ff erent EoS, was proposed by Senft &Stewart (2008). Each used EoS provides a functional form of either the Gibbsor Helmholtz free energy potential. Where the Gibbs free energyg(P,T) and Helmholtz free energy f( ρ ,T) are defined as g ( P , T ) = u ( P , T ) + P ρ ( P , T ) − T · s ( P , T ) (3) and f ( ρ, T ) = u ( ρ, T ) − T · s ( ρ, T ) . (4)As mentioned before, these potentials allow us to calculateall necessary thermodynamic properties by combination of firstand second order derivatives of g(P,T) or f( ρ ,T) (Callen 1985;Thorade & Saadat 2013). In case the EoS is formulated as aGibbs potential g(P,T) we use the relations: ρ ( P , T ) = V ( P , T ) − = (cid:32) ∂g ( P , T ) ∂ P (cid:33) − T , N , (5) s ( P , T ) = − (cid:32) ∂g ( P , T ) ∂ T (cid:33) P , N , (6) u ( P , T ) = g ( P , T ) + T · s ( P , T ) − P ρ ( P , T ) , (7) w ( P , T ) = (cid:118)(cid:117)(cid:117)(cid:117)(cid:117)(cid:116) (cid:16) ∂ g ( P , T ) ∂ T (cid:17) P , N (cid:16) ∂ g ( P , T ) ∂ T ∂ P (cid:17) N − (cid:16) ∂ g ( P , T ) ∂ T (cid:17) P , N (cid:16) ∂ g ( P , T ) ∂ P (cid:17) T , N , (8) α v ( P , T ) = (cid:32) ∂ g ( P , T ) ∂ T ∂ P (cid:33) N ρ ( P , T ) (9)and c P ( P , T ) = − T (cid:32) ∂ g ( P , T ) ∂ T (cid:33) P , N . (10)to calculate the wanted quantities. While in case of a Helmholtzfree energy potential f( ρ , T) we first solve which density corre-sponds to a given (P, T) tuple, using a bisection method and therelation P ( ρ, T ) = ρ (cid:32) ∂ f ( ρ, T ) ∂ρ (cid:33) T , N . (11)Knowing the corresponding density ρ ( P , T ) we then calculate theremaining quantities s ( ρ, T ) = − (cid:32) ∂ f ( ρ, T ) ∂ T (cid:33) ρ, N , (12) u ( ρ, T ) = f ( ρ, T ) + T · s ( ρ, T ) . (13)For w , α v and c P we first calculate K T ( ρ, T ) = ρ (cid:32) ∂ f ( ρ, T ) ∂ρ (cid:33) T , N + ρ (cid:32) ∂ f ( ρ, T ) ∂ρ (cid:33) T , N , (14) β ( ρ, T ) = ρ (cid:32) ∂ f ( ρ, T ) ∂ T ∂ρ (cid:33) N , (15)and then w ( ρ, T ) = (cid:118)(cid:117)(cid:116) K T ( ρ, T ) ρ − β ( ρ, T ) ρ (cid:16) ∂ f ( ρ, T ) ∂ T (cid:17) ρ, N , (16) α v ( ρ, T ) = β ( ρ, T ) K T ( ρ, T ) , (17) c P ( ρ, T ) = − T (cid:32) ∂ f ( ρ, T ) ∂ T (cid:33) ρ, N + T ( α v ( ρ, T ) K T ( ρ, T )) ρ K T ( ρ, T ) . (18) Article number, page 2 of 20onas Haldemann et al.: AQUA: A Collection of H O Equations of State
When using multiple EoS for the same material, special careneeds to be taken when and how to transition between EoS. Con-sidering two EoS in P–T space, two major cases need to be dis-tinguished. In the first case the two EoS describe two di ff erentphases of H O, hence a phase transition is expected to occurbetween the two EoS. The phase transition is, if present, the pre-ferred location to transition between two EoS. By definition weexpect discontinuities in the first and / or second order derivativesof the Gibbs free energy, hence no interpolation is needed totransition between two EoS. The location of the phase transitionis either taken from experimental measurements or it is locatedwhere the two Gibbs energy potentials intersect Poirier (2000).The later approach is preferential in terms of consistency, thoughit might sometimes not recover the experimentally determinedlocation of a phase transition.In the second case, no phase transition is expected to occurbetween the two EoS. One could naively think that interpolat-ing either the Gibbs or Helmholtz free energy potential of thetwo EoS and calculating all thermodynamic quantities from theinterpolated potential would then be su ffi cient. But such interpo-lation can introduce new discontinuities in the first and secondorder derivatives of the respective energy potential (see Fig. 1).Even so when using special interpolation methods as proposedby, e.g., Swesty (1996) or Baturin et al. (2019) which are thoughtto consistently evaluate tabulated EoS data, but are not thoughtfor functionally di ff erent EoS. But besides interpolating the freeenergy potentials one can also interpolate all first and secondorder derivatives independently. Doing so, the aforementioneddiscontinuities are avoided, with the draw back that the thermo-dynamic consistency will not be guaranteed, i.e., the thermody-namic variables will show deviations from Eq. (3) - (18).To illustrate this, we show in Fig. 1 a transition between twoEoS without interjacent phase transition. We see that when onlythe Gibbs free energy potential was interpolated (dashed lines),discontinuities were introduced in the entropy and specific heatcapacity. While interpolating all first and second order deriva-tives (solid lines) results in a smooth behaviour. Hence a choicebetween a smooth but slightly thermodynamic inconsistent tran-sition or a discontinuous but thermodynamic consistent transi-tion has to be made. Assuming that both EoS are valid in theirown region, we opt for the smooth transition, avoiding arbitrarilyintroduced discontinuities as shown in Fig. 1.The two aforementioned cases lead to three methods whichare used in this work to transition between EoS. The first method(in the following called Method 1) corresponds to the first casewhere a phase transition is expected between two EoS. Therewe locate the phase transition at the intersection of the Gibbsfree energy potentials and change EoS at this location. If thereis no interjacent phase transition (Method 2), then we define atransition region between the two EoS and interpolate in the firstand second order derivatives of the Gibbs energy g X ( P , T ) using g X = (1 − θ ) · g EoS X + θ · g EoS X . (19)The interpolation factor θ is calculated using either θ = ( P − P ) / ( P − P ) , (20)or θ = ( T − T ) / ( T − T ) , (21)depending on the orientation of the transition region. The lo-cation and extend of the transition region is heuristically deter-mined with the goal to reduce the introduced thermodynamic S [ k J / ( kg K )] EoS: CEA EoS: M19 T = 15000 K10 Pressure [Pa] C P [ k J / ( kg K )] Transition region independent Interpolationinterpolate Gibbs energy
Fig. 1.
Comparison between two possible methods of combining twoequation of states. The solid lines correspond to interpolating all firstand second order derivatives of the Gibbs potential independently.While for the dashed lines only the Gibbs free energy potential is in-terpolated and the derivatives are calculated thereof. inconsistencies. In case the two neighbouring EoS were con-structed such that they predict the same thermodynamic vari-ables in an overlapping region (Method 3) then no special stepsneed to be taken when transitioning between the EoS. The twoEoS can then be simply connected along a line within the overlapregion.
We just saw that combining EoS can lead to potential inconsis-tencies. We therefore attempt to use as few EoS as possible. Ina first step, the P–T space is split into seven regions for which asingle EoS is chosen. The boundaries of the regions are locatedif possible along phase transition curves. An overview over theregions is given in Table 1, where we also list which method wasused to transition to the neighbouring EoS. Fig. 2 further showshow the P–T space is split for the various EoS. The grey shadedareas in Fig. 2 show where there is no physical phase transitionbetween regions and interpolation (i.e., Method 2) is needed toassure a smooth transition of the thermodynamic variables.
The first region spans over the stability region of ice-Ih, boundedby the melting and sublimation curves as well as the ice-Ih / ice-IIphase transition curve. For ice-Ih, the EoS from Feistel & Wag-ner (2006) is the canonical reference, adopted in the IAPWS-R10-06 release. It formulates a Gibbs energy potential and bydesign has a consistent transition when for the liquid and gasphase the EoS from the IAPWS-R6-95 release is used. The lo-cation of the melting and sublimation curves is then equal to theone described in Wagner et al. (2011). For region 2 we use the EoS described in the recent work ofJournaux et al. (2020). The EoS treats the ice-II, -III, -V and -VI phases and can consistently calculate the stability region ofthe various phases. To evaluate the EoS we use the seafreeze - Article number, page 3 of 20 & A proofs: manuscript no. waterpaper
Table 1.
List of regions and the used EoS per region. As well as the method used to transition between two neighbouring regions (indicated as:region A ↔ region B: Method X). The methods 1 - 3 are listed in §2.2. Region Reference Phase Transition Method1 Feistel & Wagner (2006) ice-Ih 1 ↔
2: Method 1 1 ↔
4: Method 12 Journaux et al. (2020) ice-II, -III, -V, -VI 2 ↔
5: Method 1 2 ↔
3: Method 13 French & Redmer (2015) ice-VII, -VII*, -X 3 ↔
7: Method 24 Wagner & Pruß (2002) liquid & gas & supercritical fluid 4 ↔
5: Method 3 4 ↔
6: Method 35 Brown (2018) liquid & supercritical fluid 5 ↔
3: Method 1 5 ↔
7: Method 26 Gordon (1994); McBride (1996) gas 6 ↔
7: Method 27 Mazevet et al. (2019) supercritical fluid & superionic Temperature [K]10 P r e ss u r e [ P a ] Fig. 2.
Phase diagram of H O split into the seven regions listed in Table1. Most region boundaries (solid lines) follow phase transition curves.The dashed lines are phase transitions which are no region boundaries,i.e. the same EoS is used along the phase transition. The shaded areasshow where neighbouring regions have to be interpolated. Region 7, i.e.where the EoS of Mazevet et al. (2019) is used, expands to temperaturesup to 10 K. package of the same authors. Journaux et al. (2020) use localbasis functions to fit a Gibbs energy potential to experimentaldata. The location of the phase transitions and region bound-aries is calculated using the seafreeze -package, which also usesa Gibbs minimisation scheme to locate the phase transitions. Forthe location of the ice-VI / ice-VII phase transition we use Method1, i.e., calculating where the Gibbs potential of region 2 and 3would intersect. We find that the following fit T = x + x · ( P / Pa) + x · log( P / Pa) + x · (cid:112) ( P / Pa) (22)parameterised the location of the phase transition between ice-VIand ice-VII up to the triple point at 2.216 GPa. The coe ffi cientsof Eq. (22) can be found in Table 2. Re ff ering to the guidanceof the seafreeze package, it would be recommended to use theEoS of Bollengier et al. (2019) for the liquid phase along withthe ice phases of the seafreeze package, in order to accurately re-cover the experimental location of the melting curves. But sincethe temperature range of Bollengier et al. (2019) is restricted to500 K we choose to use Brown (2018) in the neighbouring re-gion 5. We tested if using Bollengier et al. (2019) would makea significant di ff erence for the location of the melting curve. Butchanging to Bollengier et al. (2019) for T <
500 K only shiftedthe location given by Eq. (23) by a few Kelvin. Also the evalu- https://github.com/Bjournaux/SeaFreeze Table 2.
Coe ffi cients for the fit of the melting pressure of ice-VII andice-X as well as the phase transition curve between ice-VI and ice-VII. melting ice-VII melting ice-X ice-VI / ice-VIIc 355 K 1634 . x . . − . · K x − . . . · − K x − . . . · K x . − . − . · − Kated thermodynamic variables were equal, e.g., the maximal dif-ference in density was 0.2%).
The third region is the stability region of the high pressure icephases of ice-VII and ice-X, where we use the EoS by French& Redmer (2015). They provide a Helmholtz free energy po-tential which can be evaluated in the entire stability region ofice-VII and ice-X, up to 2250 K. The melting curve which sepa-rates region 3 towards region 5 and 7 was determined minimisingthe Gibbs free energy, i.e., Method 1. We found that the meltingpressure can then be calculated using the following fitlog P melt = x · ( T / c ) x + x · ( T / c ) − + x · ( T / c ) − − . (23)Where P melt is in Pa and the coe ffi cients of x i are given in Table2. The melting curve of ice-X starts at 1634.6 K and goes up to2250 K, from where it follows an isotherm. This cut o ff at 2250K is due to the limited range of the EoS, though it is similar tothe experimental results of Schwager et al. (2004). Between 700GPa and 1.5 TPa ice-X is thought to undergo further structuralchanges until it transitions to the super-ionic phase (Militzer &Wilson 2010). Super-ionic water configurations are included inthe ab initio calculations of M19, though at higher temperaturesthan 2250 K. We tried adding also the EoS of super-ionic wateras in French et al. (2009) to our description, but no good transi-tion back to the M19-EoS was found. Therefore we decided thatfor pressures above 700 GPa we use the M19-EoS. In region 4 we use the EoS from the IAPWS-R6-95 release(Wagner & Pruß 2002), the region spans over the entire liq-uid and the cold gas phase ( < O vapour above 1273 K, we found that transitioning at 1200
Article number, page 4 of 20onas Haldemann et al.: AQUA: A Collection of H O Equations of State
K to the neighbouring region 6 results in a smooth transition(i.e., Method 3). The IAPWS-R6-95 is considered the canonicalreference EoS for H O in this P–T region, it is formulated as aHelmholtz free energy potential and reproduces well experimen-tal results.
Since pressures above 1 GPa are outside of the validity regionof the IAPWS-R6-95, we use the EoS by Brown (2018) for re-gion 5. Through the usage of local basis functions to fit a Gibbsenergy potential, Brown (2018) provide an EoS which is appro-priate for liquid and supercritical H O from 1 GPa to 100 GPaand up to 10 K. Brown (2018) used the IAPWS-R6-95 EoS, asa basis for their work, in order to transition between region 4 and5 we simply switch the EoS at the boundary. The transitions toregion 6 and 7 is discussed in their corresponding paragraph.
At low densities H O vapour can be described as an ideal gas.Though thermal e ff ects, like dissociation and thermal ionisationrequire a more complex treatment than pure ideal gas. In region6 we use the CEA (Chemical Equilibrium with Applications)package (Gordon 1994; McBride 1996), which can calculate theEoS of water at these conditions up to 2 · K, including singleionisation and thermal dissociation. Besides the thermodynamicvariables we calculate in this region also the mean molecularweight µ , the dissociation fraction x d and the ionisation fraction x ion , defined as x d = − N H O N (24)and x ion = N e N . (25)Where N is the total particle number, N H O the number of watermolecules and N e the number of electrons. The following speciesare considered when the CEA package is evaluated: H O, HO,H , H, O and O, as well as the corresponding ions. In order totransition to region 5 and 7 we use Method 2 along the transitionregion shown in Fig. 2. Region 7 corresponds to the M19-EoS. Mazevet et al. (2019)used Thomas-Fermi molecular dynamics (TFMD) simulations toconstruct a Helmholtz free energy potential up to densities of 100g / cm , which corresponds to pressures of ∼
400 TPa. Althoughthe TFMD calculations were performed up to temperatures of5 · K we consider extrapolated values until 10 K. This rangein P and T should be su ffi cient to model most of the conditionsin the interior of giant planets.Since there are no physical phase transitions between regions4 to 7 we follow Method 2 in order to transition between theEoS. We tried to find transition regions in P–T space, where thedi ff erence between neighbouring EoS is minimal. The transitionregion between regions 5 and 7 is bound towards region 5 bylog P to = log (42 GPa) + log (6 Pa) T / K −
218 (26)for temperatures between 1800 K and 4500 K, followed by anisothermal part until the boundary of region 6. While towards region 7 it is bound by 1 . · P to until 5500 K. Similar for theborder between region 6 and 7, for T > P to = log (42 GPa) + log (6 Pa) T / K −
218 (27)and 3 · P to bracket the transition region. While the transitionregion towards region 3, is between 300 and 700 GPa up to 2250K. The transition regions are indicated as grey areas in Fig. 2.We only evaluate the M19-EoS down to 300 K, hence at highpressures and T <
300 K, the M19-EoS will be evaluated at con-stant temperature. Though it is unlikely that water occurs at suchconditions anyway.
The Gibbs and Helmholtz free energy potentials, as well as theinternal energy and the entropy are relative quantities. Hencethey are defined in respect to a reference state. The IAPWS re-lease for water provides two reference states the first arbitrar-ily sets the internal energy and entropy at the triple point (P t = t = = = = = s ( P , T ) = .
13 J / (kg K) . (28)while the internal energy at the zero point is set to zero. Thismeans that for all used EoS, the entropy and energy values needto be shifted accordingly to ensure consistent transitions of theentropy and energy potentials.Since the used reference state of French & Redmer (2015)is not known, we shifted the energy potential in region 3 suchthat we recover the location of the ice-VI / VII / liquid triple pointby Wagner et al. (2011). See Table 3 for an overview of the em-ployed energy and entropy shifts. Table 3.
Overview over the energy and entropy shifts used to constructthe AQUA EoS.
Region ∆ s [J / (g K)] ∆ u [kJ / (g)]1 3.5164 0.6321287362 3.5164 0.6321287363 0.0 92.213787774 3.5164 0.6321287365 3.5164 0.6321287366 0.0 16.598954047 -0.5 -2.467871264
3. Results
In the following section we discuss the properties of the AQUA-EoS constructed with the method outlined in the last section. Wevalidate said method and compare the thermodynamic variablescalculated with the AQUA-EoS to other EoS.
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For better usability we provide tabulated values of the AQUA-EoS on P–T, ρ –T and ρ –U grids. Since the regions and theirboundaries are given in P–T, the ρ –T and ρ –u grids are derivedfrom the P–T grid. The fundamental P–T grid is calculated in thefollowing way. For every point on the grid:(1) Evaluate which region corresponds to the P,T values.(2) Calculate either the Gibbs or Helmholtz free energy giventhe regions EoS.(3) Evaluate either Eq. (5) - (10) or Eq. (11) - (18) to calculate ρ , s, u, w, ∇ Ad .(4) If the P,T values are in region 6, calculate the ionisation anddissociation fractions Eq. (25), (24) and the correspondingmean molecular weight.(5) If the P,T values are in a transition region, repeat steps (2)to (4) for the neighbouring region and transition between thetwo sets of thermodynamic variables as outlined in §2.2The tabulated AQUA-EoS is shown in Tables B.6 - B.8. Forthe P–T table, we logarithmically sampled 70 points per decadefrom 0.1 Pa to 400 TPa and 100 points per decade from 10 K to 10 K. The rho-T table shares the same spacing along thetemperature axis as the P–T table, while ρ was sampled log-arithmically with 100 points per decade from 10 − kg / m to10 kg / m . Similarly the rho–U table shares the same ρ spac-ing as the ρ -T table, while the internal energy is logarithmicallysampled with 100 points per decade from 10 J / kg to 4 · J / kg. Due to its size, the tables are published in its entirety onlyin electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/ . The tables are also available todownload under the link https://github.com/mnijh/AQUA . In order to validate the method of combining the selected EoS.We check for the thermodynamic consistency of the created tab-ulated EoS using the relation ∆ Th . c . ≡ − ρ ( T , P ) (cid:16) ∂ S ( T , P ) ∂ P (cid:17) T (cid:16) ∂ρ ( T , P ) ∂ T (cid:17) P (29)Which is a measure of how well the caloric and mechanical partof the EoS fulfil the fundamental thermodynamic relations usedto derive Eq. (5)-(18). A similar approach was chosen, e.g., inTimmes & Arnett (1999) and Becker et al. (2014). Though sincewe use P and T as natural variables for our EoS, the equationfor the thermodynamic consistency measure di ff ers from saidauthors which use ρ and T. We derived Eq. (29) from the firstlaw of thermodynamics in Appendix A. In Fig. 3 we show Eq.(29) evaluated over the P–T domain. As one can expect fromEoS based on Gibbs or Helmholtz free energy potentials, withinthe di ff erent regions our method preserves thermodynamic con-sistency. Some inconsistencies can be seen at phase transitionsbetween the ice phases as well as in the low pressure region ofice-1h, but they are rather small. The main inconsistencies are lo-cated between regions 5, 6 and 7. We would like to remind againthat we attempt to create a formulation useful over large pressureand temperature scales. If an EoS is needed which is only usedin a localised P–T domain, then other EoS will be more suitable.As already noted we evaluate the M19-EoS above 400 GPa andbelow 300 K at constant temperature, therefore in this region Temperature [K] P r e ss u r e [ P a ] l og ( | ∆ T h . c | ) Fig. 3.
Thermodynamic consistency measure δ Th . c . defined in Eq. (29),as a function of pressure and temperature. Along phase transitions, theregion boundaries and around the critical point deviations from the idealthermodynamic behaviour can be seen. The rectangular patch in the topleft originates from evaluating the M19-EoS at constant temperature. Temperature [K] P r e ss u r e [ P a ] − − − − − D e n s it y [ g / c m ] Fig. 4.
Density of H O as a function of pressure and temperature cal-culated with the collection of H O EoS of this work. The various EoSused to generate this plot are listed in Table 1. The solid black lines markthe phase transition between solid, liquid and gaseous phase. The whitedashed lines are the density contours for the region where the densityis below unity. The dot dashed black lines are adiabats calculated for a5 M ⊕ sphere of pure H O for di ff erent surface temperatures of 200 K,300 K and 1000 K. thermodynamic consistency is also not given, but again this re-gion is unlikely to be encountered in planets. Overall the methodseems to deliver consistent results for the intended purpose ofplanetary structure modelling over a wide range of pressure andtemperature. ρ ( P , T )From all studied thermodynamic variables, the ρ – P – T relationof H O will have the biggest impact on the mass radius relationof planets. In Fig. 4 we plotted ρ (P, T) using the AQUA-EoSfrom 1 Pa to 400 TPa and 150 K to 3 · K. At higher tempera-tures, anyway only the M19-EoS contributes to the AQUA-EoS,so we forwent to expand the plot to this P–T region. The solidlines show the phase boundaries while the dashed lines are thedensity contours. Overlaid are with dot-dashed lines the adia-batic P,T profiles of a 5 M ⊕ sphere of pure water for di ff erentsurface temperatures of 200 K, 300 K and 1000 K. Article number, page 6 of 20onas Haldemann et al.: AQUA: A Collection of H O Equations of State Temperature [K] P r e ss u r e [ P a ] ∆ D e n s it y [ % ] Temperature [K] P r e ss u r e [ P a ] ∆ D e n s it y [ % ] Temperature [K] P r e ss u r e [ P a ] ∆ D e n s it y [ % ] Fig. 5. Di ff erence in density between the AQUA-EoS and ANEOS (toppanel), QEOS (middle panel) and the M19-EoS (bottom panel). A pos-itive di ff erence means that the AQUA-EoS predicts a lower density inthe specific location compared to the corresponding EoS of each panel. In Fig. 5 we compare the AQUA-EoS against common EoSfor water used in planetary science, i.e. ANEOS (by Thompson(1990) using parameters for water as in Mordasini (2020)), animproved version of QEOS (priv. comm. and Vazan et al. (2013);Vazan & Helled (2020)) and against the pure M19-EoS evaluatedalso at lower pressures and temperatures. Each panel in Fig. 5shows the density di ff erence in percent between the AQUA-EoSand the corresponding EoS of each panel calculated using ∆ ρ ( T , P )) = · ρ i ( T , P ) − ρ AQUA ( T , P ) ρ AQUA ( T , P ) . (30)Where the index i represents the EoS against which the dif-ference in density is calculated. We note that both ANEOSand QEOS predict consistently lower densities at high pressures ( >
10 GPa). In contrary the density of ice-Ih is predicted higherthan in the AQUA-EoS or as in Feistel & Wagner (2006). Inthe gas phase below 1 GPa ANEOS predicts continuously lowerdensities, similar di ff erences are seen for QEOS except above2000 K where QEOS predicts slightly larger densities. QEOShas a significant shift in the location of the vapour curve and thelocation of the critical point.For comparison we also evaluated the M19-EoS over thesame P–T range. As expected no di ff erence is seen at high pres-sures, since the same EoS is evaluated. At low pressures the den-sity di ff erence in the ice phases is visible and also the large dif-ferences in the gaseous low density regions below 1 GPa. ∇ Ad ( P , T )The dimensionless adiabatic temperature gradient ∇ Ad ( P , T ) is akey quantity to study the convective heat transport of a planet.In Fig. 6 we show the ∇ Ad ( P , T ) of the AQUA-EoS, ANEOS andQEOS. Compared to the the AQUA-EoS, the adiabatic gradi-ent of ANEOS in the ice-Ih, liquid and cold gas phase is sim-ilar, while QEOS shows a larger gradient and a shifted vapourcurve. In the gas phase, ANEOS shows a region of low adiabaticgradient between 1000K and 1100K. While for AQUA-EoS asimilar feature caused by the thermal dissociation is visible butat higher temperatures. At the same time ANEOS does not in-clude thermal ionisation e ff ects which cause the second depres-sion of ∇ Ad in AQUA between 6000 K and 10000 K. In QEOSnone of these features are present. Since in both AQUA-EoS andANEOS, the liquid and low pressure ice regions ∇ Ad ( P , T ) isclose to zero. This will lead to an almost isothermal tempera-ture profile. Therefore any adiabatic temperature profile start-ing in one of these regions will stay in its solid or liquid stateuntil it eventually reaches the high pressure ices phases. Start-ing in the vapour phase will cause the temperature profile to besteep enough to remain in the vapour phase and then transitionto the supercritical region. All EoS show numerical artefacts atlow temperatures and high pressure, though it is unlikely thatplanetary models will need this part of P–T space. s ( P , T ) , internal energy u ( P , T )As with the other variables we compare the results of the entropyand internal energy calculations with predictions by ANEOS andQEOS. In Fig. 7 and 8 we show in the top panel the entropy andinternal energy predictions by AQUA as a function of P and T .While in the middle panel we show the relative di ff erences com-pared to ANEOS and in the bottom panel compared to QEOS.The di ff erences are calculated in the same way as for the densityin Eq. (30). Compared to ANEOS the largest di ff erences occurin the region where H O dissociates. Both entropy and energydi ff er in this region by a factor of two. For the other part in P–Tspace the results for the internal energy do not di ff er more than ±
25 %. Except a small region in the high pressure ice phases.Contrary the entropy of ANEOS is significantly higher in the re-gion of the high pressure ices between 10 and 10 Pa. Likelydue to the fact that the location of the melting curve in ANEOSis at much lower temperature than the one of AQUA.While the energies and entropies of ANEOS were alwayswithin the same order of magnitude. The predictions of QEOSseem to be globally shifted. Compared to AQUA the energiesare in average ∼ / g larger while the entropies are ∼ / (gK) smaller. This shift likely originates from a di ff erent choice ofreference state. Though since this information is not provided in Article number, page 7 of 20 & A proofs: manuscript no. waterpaper Temperature [K] P r e ss u r e [ P a ] ∇ A d Temperature [K] P r e ss u r e [ P a ] ∇ A d Temperature [K] P r e ss u r e [ P a ] ∇ A d Fig. 6.
Adiabatic temperature gradient of ANEOS (top panel), QEOS(bottom panel) and the AQUA-EoS (bottom panel) as a function of pres-sure and temperature. The black lines are the phase boundaries as in Fig.4.
Vazan et al. (2013), we can not be certain. Hence for most part ofP–T space, the entropies of QEOS are 50%-75% smaller than theones of AQUA. Only in the low temperature vapour region theentropy is a few percent larger. Regarding the internal energies,a shift of 37.5 kJ / g means that for pressures below ∼ Paand temperature below ∼ ff er by multiple orders of magnitude. Assuming thatthis shift is due to a di ff erent reference state we show in Fig. 8the di ff erence in energy if the internal energy potential of QEOSwould be 37.5 kJ / g smaller. We see that compared to ANEOS thespread in di ff erences is larger. Some di ff erences can be attributedto the shifted vapour curve. While we do not see a strong e ff ectof the melting curve as we do with ANEOS. Though the energyof ice VI is notably smaller than the energy of ice VII and theother low pressure ices. Due to the applied shift in energy, the Temperature [K] P r e ss u r e [ P a ] E n t r opy [ k J / ( kg K )] Temperature [K] P r e ss u r e [ P a ] ∆ E n t r opy [ % ] Temperature [K] P r e ss u r e [ P a ] ∆ E n t r opy [ % ] Fig. 7.
In the top panel the specific entropy of AQUA as a function ofpressure and temperature is shown. In the middle panel we show therelative di ff erence between the specific entropy of ANEOS vs. AQUA.While in the bottom panel the same comparison is performed betweenQEOS and AQUA. di ff erences especially at low pressures can not be accurately de-termined. w ( P , T )At last we show the results for the bulk speed of sound. SinceQEOS of Vazan et al. (2013) does not provide the bulk speed ofsound we will compare in Fig. 9 only against ANEOS. Thoughin Fig. 10 we also show a comparison against experimental re-sults of Lin & Trusler (2012) at low temperatures. Comparedto ANEOS the bulk speed of sound is for most parts within ± ff erences occur throughout the dissociation re-gion, around the critical point and within the region of ice-Ih. At Article number, page 8 of 20onas Haldemann et al.: AQUA: A Collection of H O Equations of State Temperature [K] P r e ss u r e [ P a ] l og E n e r gy [ k J / g ] Temperature [K] P r e ss u r e [ P a ] ∆ E n e r gy [ % ] Temperature [K] P r e ss u r e [ P a ] ∆ E n e r gy [ % ] Fig. 8.
In the top panel the specific internal energy of AQUA as afunction of pressure and temperature is shown. In the middle panel weshow the relative di ff erence between the internal energy of ANEOS vs.AQUA. While in the bottom panel the same comparison is performedbetween QEOS and AQUA. The internal energy potential of QEOSseems to be globally shifted compared to ANEOS and AQUA. Prob-ably due to a di ff erent choice of reference state. For the comparison wetherefore subtracted 37.5 kJ / g from u(T,P) QEOS . high pressures ( > Pa) both ANEOS and AQUA results arewithin 10 %.In Fig. 10 one can see that due to the use of the IAPWS-95EoS the bulk speed of sound of AQUA (solid lines) fits very wellthe experimental data of Lin & Trusler (2012). While ANEOS(dashed lines) over predicts the speed of sound at pressures be-low 10 Pa. Also ANEOS does not show a drop in speed of soundat the vapour curve. For comparison we also show what the pureM19-EoS would predict (dotted lines). Like ANEOS it showsno drop at the vapour curve while predicting a generally lowerspeed of sound than AQUA. Temperature [K] P r e ss u r e [ P a ] ∆ w [ % ] Fig. 9.
Relative di ff erence between the bulk speed of sound of ANEOSand AQUA as a function of pressure and temperature. The black dotsindicate the location of the experimental data of Lin & Trusler (2012)shown in Fig. 10. Pressure [Pa]1000120014001600180020002200 w [ m / s ] AQUA (IAPWS-95)ANEOSM19-EoSLin & Trusler 2012 T: 303 KT: 333 KT: 413 KT: 473 K
Fig. 10.
Comparison of the bulk speed of sound, between AQUA-EoS(solid), ANEOS (dashed), the pure M19-EoS (dotted) and experimentalresults of Lin & Trusler (2012). We would like to point out that the com-pared range corresponds to region 4 and 5. Hence AQUA-EoS evaluatesmainly the IAPWS-95 EoS and above 10 Pa the EoS of Brown (2018)is used.
4. Effect on the Mass Radius Relation of Planets
We see the main application of the AQUA-EoS in the calculationof internal structures of planets, exoplanets and their moons. Totest the e ff ect of di ff erent EoS onto these calculations, we deter-mine the mass radius relation for pure water spheres. As alreadyMazevet et al. (2019) stated, this is a purely academic exercise,but it is still useful since the results solely depend on the usedEoS. In Appendix B we explain how we calculate the internalstructure of a pure water sphere of given mass and determineits radius. We compare the AQUA-EoS against ANEOS, QEOS,the H O EoS used in Sotin et al. (2007) and the mass radiusresults of Zeng et al. (2019). Zeng et al. (2019) use a similarselection of EoS to the one proposed in this work i.e. Wagner& Pruß (2002), Frank et al. (2004), French et al. (2009) andFrench & Redmer (2015) but do not provide a public availableEoS. Though we will use their results as a benchmark for ourmass radius calculations. A more simple approach was chosenby Sotin et al. (2007), which on the other hand use two 3rd or-der Birch-Murnaghan EoS: one isothermal for the liquid layerand one including temperature corrections for the high pressureices. In Fig. 11 we show the result of the structure calculations
Article number, page 9 of 20 & A proofs: manuscript no. waterpaper
ANEOS Zeng et al. 2019 QEOS Sotin et al. 2007 This work M ⊕ ]1.01.52.02.53.03.5 R a d i u s [ R ⊕ ] T surf = 300 K 0 5 10 15 20Mass [ M ⊕ ]1.01.52.02.53.03.5 R a d i u s [ R ⊕ ] T surf = 500 K0 5 10 15 20Mass [ M ⊕ ]1.01.52.02.53.03.5 R a d i u s [ R ⊕ ] T surf = 700 K 0 5 10 15 20Mass [ M ⊕ ]1.01.52.02.53.03.5 R a d i u s [ R ⊕ ] T surf = 1000 K Fig. 11.
The mass radius relations of isothermal spheres in hydrostatic equilibrium made of 100 wt% H O (solid lines) or 50 wt% H O and 50wt% Earth like composition as in Zeng et al. (2019) (dashed lines), for di ff erent EoS and di ff erent surface temperatures T surf . The surface pressurewas chosen to be 1 mbar as in Zeng et al. (2019). For the cases with Earth like composition we used Hakim et al. (2018) as EoS for the Fe andSotin et al. (2007) to calculate the density in the MgSiO layer. In the top left panel also the Earth like composition case is plotted (dotted lines) inorder to quantify the contribution from the underlying rocky part to the cases of mixed composition. for isothermal water spheres with masses between 0.25 and 20 M ⊕ . As in Zeng et al. (2019) we fixed the surface pressure to 1mbar, while each panel shows the results for a di ff erent surfacetemperature between 300 K and 1000 K.We see that the choice of EoS has a strong e ff ect on the ra-dius for a given water mass. For ANEOS and QEOS one canpredict that for large water mass fractions the radii for a givenmass will be bigger, due to the lower density at high pressures.This feature is visible in all panels. The results of ANEOS arecloser to AQUA, than the ones of QEOS. For both the change insurface temperature does not strongly a ff ect the relative di ff er-ences compared to AQUA. Contrary the EoS used in Sotin et al.(2007) shows a bigger di ff erence towards higher temperatures.This is due to the isothermal liquid layer and the absence of avapour description in Sotin et al. (2007). But at 300 K the resultsonly di ff er by -0.8% to -3.69% for Sotin et al. (2007).We report that the mass radius relation of Zeng et al. (2019)does predict very similar radii, within ± . / super-ionicphase, as soon as the isotherm would intersect the melting curve.Which would lead to lower densities at high pressures.The particular kink in the various mass radius relation at highsurface temperatures and low water masses originates from thefact that there is not enough mass to create a steep enough pres- sure profile and for high enough temperatures the water sphereis then almost completely in the vapour phase, which results ininflated radii. This e ff ect would be much more pronounced if anadiabatic temperature gradient was used, where even for lowersurface temperatures the temperature profile would not cross thevapour curve.For comparison we also plotted in dashed lines the mass ra-dius relation for spheres with a 50 wt% H O and 50 wt% Earthlike composition (i.e. 33.75 wt% MgSiO and 16.25 wt% Fe), asin Zeng et al. (2019). The results are also listed in Table B.5 inthe appendix. For the EoS of the Fe core we used Hakim et al.(2018) and Sotin et al. (2007) for the MgSiO layer. In the 300K panel we show as dotted lines also the pure Earth like com-position case, in order to show that any di ff erence in the 50 wt%H O case stems from the H O EoS. The di ff erence in radius forthe 50 wt% H O case are about a factor two smaller than thedi ff erence in the pure H O case, i.e. between -1% and 1.1% ofrelative di ff erence. For planets with significant amounts of volatile elements theproper treatment of thermal transport is of big importance forthe mass radius calculation. We show here the e ff ect of having afully adiabatic temperature profile instead of an isothermal one,as it was assumed in the last section. Article number, page 10 of 20onas Haldemann et al.: AQUA: A Collection of H O Equations of State
Table 4.
Tabulated radii of a pure water spheres using either an adiabatictemperature gradient (Radius Ad ) or an isothermal temperature profile(Radius i.t.s ) and various surface temperatures. The surface pressure waschosen as in section 5.1 of Mazevet et al. (2019), i.e., either along thevapour curve or if the temperature was supercritical fixed at 1 bar. T surf [K] Radius Ad [R ⊕ ] Radius i.t. [R ⊕ ] δ R [%]Mass = ⊕ = ⊕ ff erence we choose as in Sect.5.1 of Mazevet et al. (2019) two masses of 0 . ⊕ and 5 M ⊕ .For various surface temperatures we calculate the structure ofa pure H O sphere. We use the same model as in the last sec-tion, although we set the surface pressure to either the value ofthe vapour curve or 1 bar if above the critical temperature (as inMazevet et al. (2019)). We show in Fig. 12 the density as a func-tion of radius for said two masses. We see that considering thetwo thermal structures, the density profile is considerably di ff er-ent at large surface temperatures (T surf > surf <
300 K) it is almost equal. In theadiabatic case starting at 2000 K it is even below 2 · − g / cm throughout the structure. Here we see the e ff ect of increased adi-abatic temperature gradient in the vapour phase compared to theliquid or solid phases. This e ff ect is reduced if the water massbecomes larger and hence the sampled pressure scale increasessimultaneously. In Table (4) we list the total radii of all casesshown in Fig. 12.One has to remember that these results are based on calcula-tions of pure water spheres, any addition of dense material willcause a steeper pressure profile and hence a more compact ra-dius. We still conclude that the choice of thermal transport hasa significant e ff ect on the mass radius relation of a volatile layermade out of H O.
5. Conclusions
We combined the H O-EoS from Mazevet et al. (2019) withthe EoS of Feistel & Wagner (2006); Journaux et al. (2020)and French & Redmer (2015) to include the description of icephases at low, intermediate and high pressures. For a propertreatment of the liquid phase and gas phase at low pressures R ⊕ ]0.00.51.01.52.02.5 ρ [ g / c m ] Mass = 0.5 M ⊕ R ⊕ ]012345 ρ [ g / c m ] Mass = 5.0 M ⊕ Fig. 12.
Density profiles of a water sphere using either an isother-mal temperature profile (solid) or an adiabatic temperature gradient(dashed). The surface temperatures are set to four di ff erent values (black =
300 K, green =
500 K, blue = = we added the EoS by Brown (2018); Wagner & Pruß (2002)and the CEA package (Gordon 1994; McBride 1996) for thehigh temperature low pressure region. This resulted in the tabu-lated AQUA-EoS (which is available at https://github.com/mnijh/aqua ) providing data for the density ρ , adiabatic temper-ature gradient ∇ Ad , specific entropy s , specific internal energy u and bulk speed of sound w . As well as mean molecular weight µ , ionisation fraction x i and dissociation fraction x d for a limitedregion. The AQUA-EoS o ff ers a multi phase description of allmajor phases of H O useful to model the interiors of planets andexoplanets. We recommend the AQUA-EoS for use cases wherethermodynamic data over a large range of pressures and temper-atures is needed. Though, by its construction, AQUA-EoS is notfully thermodynamical consistent since it is not calculated froma single energy potential, but consistency is su ffi cient for a largepart in P–T space. Nevertheless we remind the reader again, thatwe do not intend to o ff er a more accurate description than anyEoS tailored to a limited region in P–T space but rather an EoSvalid over a larger range of thermodynamical values.We compared the values of the thermodynamics variablesderived from the AQUA-EoS against the values from ANEOS(Thompson 1990) and QEOS (Vazan et al. 2013; Vazan & Helled2020). Compared to ANEOS and QEOS, AQUA shows a largerdensity at P >
10 GPa, an e ff ect which is already present in the Article number, page 11 of 20 & A proofs: manuscript no. waterpaper original M19-EoS. At lower pressures the largest di ff erence areseen in the region of ice-Ih and in the gas below 2000 K. For ∇ Ad the results are more similar though not identical. For the entropy s and also the internal energy u , ANEOS predicts higher val-ues by a factor two throughout the dissociation region and alongthe melting curve of ice-Ih. While in most other regions s and u only di ff ers by ∼
25% compared to AQUA. Except within theice-VII and ice-X region where the entropy is larger by a factortwo given a vastly colder melting curve of ice-VII / X in ANEOS.QEOS shows in average a ∼ / (g K) lower entropy than AQUA.Also the internal energy potential u of QEOS seems shifted by37.5 kJ / g. Given that it is unclear if this shifts stems from a dif-ferent reference point, the comparison of s and u to AQUA arelikely not very accurate. For the bulk speed of sound w we com-pared against ANEOS and experimental values of Lin & Trusler(2012), since QEOS does not provide this thermodynamic quan-tity. ANEOS shows the largest di ff erences at pressures below 10 Pa. While given the use of the IAPWS-95 release, AQUA agreesvery well with the results of Lin & Trusler (2012).We further studied the e ff ect of di ff erent EoS on the massradius relation of pure H O spheres. Within ± .
5% we repro-duce the values of Zeng et al. (2019) which use a similar selec-tion of EoS. The other tested EoS (ANEOS, QEOS and Sotinet al. (2007)) show much bigger deviations from the radii wecalculated. Deviations are between 3% and 8 % for ANEOS andbetween 7% and 14% for QEOS, excluding the low water masscases ( ≤ . ⊕ ) where the di ff erences for high temperatures canbe larger than 10%. The H O EoS of Sotin et al. (2007) is mainlysuited for low surface temperatures since it does not incorporateany vapour phase. For surface temperatures around 300 K it con-sistently predicts a smaller radius for a given mass by -0.8% to-3.6%. Even though we focused in this part on isothermal struc-tures of pure water spheres, which is a mere theoretical test. Thedi ff erences between EoS are still significant, especially in theview of improved radius estimates from upcoming space basedtelescopes such as CHEOPS (Benz et al. 2017) or PLATO (Rauer& Heras 2018). Future work will be needed to unify the descrip-tion of the thermodynamic properties of water over a wide rangeof pressure and temperatures.In a last part we showed that the e ff ect of surface temperatureon the total radius is much bigger when we assume an adiabatictemperature profile instead of an isothermal one. This empha-sises the importance of a proper treatment of the thermal partof the used EoS when modelling the structure of volatile richplanets. Acknowledgements.
We thank the anonymous referee for their valuablecomments. We also thank Julia Venturini for the help implementing theCEA code and for various fruitful discussions. Further, we would like tothank Allona Vazan to provide to us her updated QEOS table for H O. J.H.acknowledges the support from the Swiss National Science Foundation undergrant 200020_172746 and 200020_19203. C.M. acknowledges the supportfrom the Swiss National Science Foundation from grant BSSGI0_155816“PlanetsInTime”.
Software.
For this publication the following software packages have beenused: Python 3.6, CEA (Chemical Equilibrium with Applications) (Gordon1994; McBride 1996), Python-iapws, Python-numpy, Python-matplotlib,Python-scipy, Python-seaborn, Python-seafreeze.(Journaux et al. 2020)
References
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Article number, page 12 of 20onas Haldemann et al.: AQUA: A Collection of H O Equations of State
Appendix A: Derivation of the thermodynamicconsistency measure
Unlike other authors which use ρ and T as natural variablesfor their EoS we choose to use P and T instead. Therefore thethermodynamic consistency measure used e.g. in Becker et al.(2014) needs to be reformulated for the use of P and T as naturalvariables. We start with the fundamental thermodynamic relationin terms of the internal energy U, i.e. dU ( T , P ) = T dS ( T , P ) − PdV ( T , P ) . (A.1)Then we replace the di ff erentials of the internal energy, entropyand the volume with the following relations dS ( T , P ) = (cid:32) ∂ S ( T , P ) ∂ T (cid:33) P dT + (cid:32) ∂ S ( T , P ) ∂ P (cid:33) T dP (A.2) dV ( T , P ) = (cid:32) ∂ V ( T , P ) ∂ T (cid:33) P dT + (cid:32) ∂ V ( T , P ) ∂ P (cid:33) T dP (A.3) dU ( T , P ) = (cid:32) ∂ U ( T , P ) ∂ T (cid:33) P dT + (cid:32) ∂ U ( T , P ) ∂ P (cid:33) T dP (A.4)and sort the pressure and temperature derivatives to one side ofthe equation each (cid:32) ∂ U ( T , P ) ∂ T (cid:33) P dT − T (cid:32) ∂ S ( T , P ) ∂ T (cid:33) P dT + P (cid:32) ∂ V ( T , P ) ∂ T (cid:33) P dT = − (cid:32) ∂ U ( T , P ) ∂ P (cid:33) T dP + T (cid:32) ∂ S ( T , P ) ∂ P (cid:33) T dP − P (cid:32) ∂ V ( T , P ) ∂ P (cid:33) T dP . (A.5)Using Bridgman’s thermodynamic equations (Bridgman 1914)we can replace some of the partial derivatives using the follow-ing relations (cid:32) ∂ U ( T , P ) ∂ T (cid:33) P = C P − P (cid:32) ∂ V ( T , P ) ∂ T (cid:33) P (A.6) (cid:32) ∂ S ( T , P ) ∂ T (cid:33) P = C P ( T , P ) T (A.7) (cid:32) ∂ U ( T , P ) ∂ P (cid:33) T = − T (cid:32) ∂ V ( T , P ) ∂ T (cid:33) P − P (cid:32) ∂ V ( T , P ) ∂ P (cid:33) T . (A.8)Hence Eq. (A.5) can be written as0 = T (cid:32) ∂ V ( T , P ) ∂ T (cid:33) P dP + T (cid:32) ∂ S ( T , P ) ∂ P (cid:33) T dP . (A.9)Next, we can divide both sides by T · dP which results in one ofthe Maxwell relations (cid:32) ∂ S ( T , P ) ∂ P (cid:33) T = − (cid:32) ∂ V ( T , P ) ∂ T (cid:33) P = ρ ( T , P ) (cid:32) ∂ρ ( T , P ) ∂ T (cid:33) P . (A.10)Similar to Becker et al. (2014) we define a measure of thermo-dynamic consistency, which compares the caloric left hand sideof Eq.(A.10) with the mechanical right hand side: ∆ Th . c . ≡ − ρ ( T , P ) (cid:16) ∂ S ( T , P ) ∂ P (cid:17) T (cid:16) ∂ρ ( T , P ) ∂ T (cid:17) P . (A.11) Appendix B: Structure model
To determine the mass radius relation for pure H O spheres (or50 wt% H O when compared to Zeng et al. (2019)), we solvethe mechanical an thermal structure equations in the Lagrangiannotation, as in Kippenhahn et al. (2012) for stellar structures. Weassume a constant luminosity throughout the structure, i.e. weneglect potential heat sources within the planet. The remainingstructure equations for a static, 1D-spherically symmetric spherein hydrostatic equilibrium are then given by ∂ r ∂ m = π r ρ , (B.1) ∂ P ∂ m = − Gm π r , (B.2) ∂ T ∂ m = ∂ P ∂ m TP ∇ Ad (B.3)where ∇ Ad is the adiabatic temperature gradient as defined inEq. (2), r is the radius, m is the mass within radius r, P is thepressure and T the temperature. For a given total mass, surfacepressure and surface temperature we use a bidirectional shootingmethod to solve the two point boundary value problem, posed byEqs. (B.1)-(B.3). The equations are integrated using a 5th orderCash-Karp Runge-Kutta method, similar to the one described inPress et al. (1996). From this calculation we get the mechanicaland thermal structure as a function of m . From which we canextract the total radius at m = M tot . If not stated di ff erently thesurface pressure is set to 1 mbar as in Zeng et al. (2019), whichis a first order approximation of the depth of the transit radius.At each numerical step in the Runge-Kutta method, the equa-tion of state is evaluated to determine ρ ( P , T ) and ∇ Ad ( P , T ). Foran isothermal structure ∇ Ad ( P , T ) is simply set to zero. As de-scribed in the main text we test various water equation of state.In the case where we compare with the results of Zeng et al.(2019) we split the structure into three layers, an iron core usingthe EoS of Hakim et al. (2018) (16.25 wt%), a silicate mantle asin Sotin et al. (2007) (33.75 wt%) and a water layer (50 wt%).Similar to this work, Zeng et al. (2019) use multiple EoS forthe water layer, i.e. Wagner & Pruß (2002), Frank et al. (2004),French et al. (2009) and French & Redmer (2015). Article number, page 13 of 20 & A proofs: manuscript no. waterpaper
Table B.1.
Mass radius relation for isothermal pure H O spheres and various EoS. The surface boundary conditions are T Surf =
300 K and P Surf = AQUA ANEOS Zeng et al. (2019) QEOS Sotin et al. (2007)Mass [M ⊕ ] Radius [R ⊕ ] Radius [R ⊕ ] δ R [%] Radius [R ⊕ ] δ R [%] Radius [R ⊕ ] δ R [%] Radius [R ⊕ ] δ R [%]0.10 0.768 0.819 6.58 0.726 -5.52 0.763 -0.62 0.719 -6.360.25 0.978 1.019 4.20 0.953 -2.53 1.033 5.63 0.942 -3.600.50 1.178 1.222 3.71 1.161 -1.46 1.298 10.12 1.152 -2.261.00 1.416 1.474 4.15 1.41 -0.42 1.594 12.58 1.398 -1.251.50 1.573 1.647 4.66 1.577 0.24 1.777 12.92 1.56 -0.862.00 1.696 1.781 4.99 1.705 0.51 1.921 13.28 1.682 -0.792.50 1.798 1.891 5.20 1.811 0.71 2.042 13.56 1.782 -0.883.00 1.886 1.986 5.33 1.903 0.94 2.145 13.73 1.866 -1.033.50 1.963 2.07 5.44 1.981 0.91 2.233 13.75 1.94 -1.194.00 2.032 2.145 5.52 2.053 0.99 2.31 13.67 2.005 -1.374.50 2.095 2.212 5.58 2.117 1.02 2.379 13.54 2.063 -1.545.00 2.153 2.275 5.63 2.176 1.04 2.442 13.39 2.116 -1.726.00 2.257 2.385 5.70 2.282 1.13 2.552 13.09 2.21 -2.057.00 2.347 2.482 5.76 2.372 1.06 2.648 12.82 2.292 -2.348.00 2.427 2.568 5.83 2.451 1.01 2.733 12.61 2.364 -2.589.00 2.498 2.646 5.92 2.526 1.11 2.809 12.44 2.429 -2.7710.0 2.562 2.717 6.05 2.59 1.07 2.878 12.32 2.488 -2.9012.0 2.672 2.843 6.42 2.707 1.32 2.999 12.25 2.592 -2.9814.0 2.764 2.952 6.82 2.809 1.62 3.102 12.25 2.682 -2.9616.0 2.844 3.049 7.20 2.896 1.83 3.193 12.26 2.762 -2.9118.0 2.916 3.136 7.55 2.973 1.98 3.273 12.27 2.833 -2.8420.0 2.98 3.214 7.88 3.046 2.22 3.346 12.28 2.898 -2.75 Article number, page 14 of 20onas Haldemann et al.: AQUA: A Collection of H O Equations of State
Table B.2.
Mass radius relation for isothermal pure H O spheres and various EoS. The surface boundary conditions are T Surf =
500 K and P Surf = AQUA ANEOS Zeng et al. (2019) QEOS Sotin et al. (2007)Mass [M ⊕ ] Radius [R ⊕ ] Radius [R ⊕ ] δ R [%] Radius [R ⊕ ] δ R [%] Radius [R ⊕ ] δ R [%] Radius [R ⊕ ] δ R [%]0.10 1.062 1.253 18.04 1.065 0.28 0.971 -8.52 0.717 -32.450.25 1.148 1.235 7.57 1.145 -0.28 1.168 1.70 0.942 -17.950.50 1.299 1.368 5.28 1.296 -0.23 1.397 7.56 1.152 -11.291.00 1.502 1.577 4.99 1.505 0.16 1.668 11.03 1.399 -6.851.50 1.645 1.732 5.29 1.654 0.59 1.839 11.85 1.561 -5.062.00 1.758 1.855 5.52 1.772 0.78 1.976 12.4 1.684 -4.212.50 1.854 1.958 5.65 1.871 0.92 2.09 12.75 1.784 -3.783.00 1.937 2.048 5.74 1.958 1.09 2.187 12.93 1.868 -3.573.50 2.011 2.127 5.80 2.032 1.05 2.272 12.98 1.941 -3.474.00 2.077 2.199 5.85 2.10 1.11 2.346 12.95 2.006 -3.434.50 2.138 2.264 5.89 2.163 1.16 2.413 12.88 2.064 -3.435.00 2.194 2.324 5.92 2.219 1.17 2.474 12.79 2.118 -3.466.00 2.294 2.43 5.96 2.321 1.19 2.582 12.57 2.212 -3.577.00 2.381 2.524 6.00 2.408 1.11 2.676 12.37 2.293 -3.708.00 2.459 2.608 6.05 2.485 1.06 2.759 12.18 2.365 -3.829.00 2.529 2.684 6.12 2.558 1.16 2.833 12.04 2.43 -3.9010.0 2.591 2.753 6.23 2.62 1.12 2.901 11.95 2.489 -3.9512.0 2.698 2.876 6.57 2.735 1.34 3.02 11.9 2.593 -3.9114.0 2.789 2.983 6.95 2.833 1.60 3.121 11.92 2.683 -3.8016.0 2.868 3.078 7.31 2.921 1.84 3.211 11.95 2.762 -3.6818.0 2.938 3.163 7.64 2.996 1.97 3.29 11.97 2.834 -3.5520.0 3.001 3.24 7.95 3.067 2.18 3.361 11.99 2.898 -3.43 Table B.3.
Mass radius relation for isothermal pure H O spheres and various EoS. The surface boundary conditions are T Surf =
700 K and P Surf = AQUA ANEOS Zeng et al. (2019) QEOS Sotin et al. (2007)Mass [M ⊕ ] Radius [R ⊕ ] Radius [R ⊕ ] δ R [%] Radius [R ⊕ ] δ R [%] Radius [R ⊕ ] δ R [%] Radius [R ⊕ ] δ R [%]0.25 1.376 1.601 16.36 1.382 0.45 1.437 4.43 0.894 -35.050.50 1.445 1.567 8.47 1.462 1.17 1.571 8.75 1.10 -23.851.00 1.601 1.703 6.41 1.615 0.91 1.786 11.54 1.355 -15.341.50 1.724 1.831 6.26 1.743 1.13 1.935 12.27 1.523 -11.622.00 1.826 1.94 6.27 1.847 1.18 2.058 12.73 1.65 -9.602.50 1.914 2.034 6.27 1.938 1.22 2.163 13.0 1.753 -8.403.00 1.992 2.117 6.27 2.019 1.34 2.253 13.11 1.84 -7.633.50 2.062 2.191 6.27 2.088 1.29 2.332 13.12 1.915 -7.104.00 2.125 2.258 6.28 2.153 1.32 2.403 13.08 1.982 -6.724.50 2.183 2.32 6.28 2.211 1.30 2.466 12.99 2.042 -6.455.00 2.236 2.377 6.28 2.265 1.29 2.525 12.89 2.096 -6.266.00 2.333 2.479 6.27 2.364 1.33 2.628 12.66 2.192 -6.017.00 2.418 2.569 6.27 2.447 1.23 2.718 12.44 2.275 -5.878.00 2.493 2.65 6.29 2.522 1.15 2.798 12.25 2.349 -5.799.00 2.561 2.723 6.34 2.592 1.21 2.871 12.09 2.415 -5.7110.0 2.622 2.79 6.43 2.652 1.16 2.936 11.98 2.474 -5.6212.0 2.726 2.91 6.74 2.763 1.36 3.051 11.92 2.58 -5.3814.0 2.815 3.014 7.09 2.861 1.62 3.151 11.92 2.671 -5.1216.0 2.892 3.107 7.42 2.945 1.82 3.238 11.93 2.751 -4.8818.0 2.961 3.191 7.74 3.019 1.94 3.315 11.95 2.823 -4.6620.0 3.024 3.266 8.03 3.089 2.15 3.385 11.95 2.889 -4.46 Article number, page 15 of 20 & A proofs: manuscript no. waterpaper
Table B.4.
Mass radius relation for isothermal pure H O spheres and various EoS. The surface boundary conditions are T Surf = P Surf = AQUA ANEOS Zeng et al. (2019) QEOS Sotin et al. (2007)Mass [M ⊕ ] Radius [R ⊕ ] Radius [R ⊕ ] δ R [%] Radius [R ⊕ ] δ R [%] Radius [R ⊕ ] δ R [%] Radius [R ⊕ ] δ R [%]0.25 1.842 6.42 248.45 1.866 1.28 2.29 24.27 0.887 -51.860.50 1.696 2.039 20.22 1.711 0.87 1.966 15.89 1.038 -38.821.00 1.766 1.950 10.46 1.795 1.68 2.008 13.74 1.205 -31.761.50 1.852 2.015 8.82 1.887 1.90 2.106 13.74 1.350 -27.092.00 1.934 2.093 8.20 1.970 1.87 2.202 13.87 1.473 -23.822.50 2.009 2.167 7.84 2.045 1.78 2.289 13.9 1.578 -21.463.00 2.078 2.236 7.60 2.115 1.76 2.366 13.85 1.669 -19.683.50 2.141 2.300 7.43 2.177 1.66 2.435 13.75 1.75 -18.284.00 2.199 2.359 7.31 2.235 1.65 2.498 13.63 1.822 -17.154.50 2.252 2.414 7.21 2.288 1.61 2.556 13.49 1.887 -16.225.00 2.302 2.466 7.13 2.339 1.60 2.609 13.35 1.946 -15.456.00 2.392 2.560 7.00 2.429 1.54 2.705 13.06 2.052 -14.247.00 2.473 2.643 6.91 2.507 1.40 2.789 12.78 2.143 -13.338.00 2.545 2.719 6.86 2.578 1.32 2.864 12.55 2.223 -12.629.00 2.609 2.788 6.85 2.645 1.36 2.932 12.35 2.296 -12.0210.0 2.668 2.852 6.90 2.702 1.29 2.994 12.21 2.361 -11.512.0 2.769 2.966 7.12 2.808 1.43 3.103 12.09 2.476 -10.5714.0 2.854 3.066 7.41 2.901 1.64 3.198 12.05 2.575 -9.8016.0 2.929 3.155 7.70 2.983 1.82 3.282 12.03 2.661 -9.1518.0 2.996 3.235 7.98 3.054 1.93 3.356 12.01 2.739 -8.5920.0 3.057 3.309 8.24 3.122 2.12 3.424 12.0 2.809 -8.12 Article number, page 16 of 20onas Haldemann et al.: AQUA: A Collection of H O Equations of State
Table B.5.
Mass radius relation for isothermal spheres with 50 wt% H O, 33.75 wt% MgSiO and 16.25 wt% Fe. Radius A was calculated usingAQUA-EoS for the H O, the EoS from Sotin et al. (2007) for the MgSiO3 and the EoS from Hakim et al. (2018) for Fe. Radius Z is based on theresults from Zeng et al. (2019). The surface pressure is P Surf = T surf
300 K 500 KMass [M ⊕ ] Radius A [R ⊕ ] Radius Z [R ⊕ ] δ R [%] Radius A [R ⊕ ] Radius Z [R ⊕ ] δ R [%]0.50 1.028 1.018 -1.01 1.117 1.118 0.091.00 1.247 1.241 -0.49 1.312 1.314 0.121.50 1.389 1.387 -0.16 1.444 1.448 0.302.00 1.499 1.502 0.21 1.546 1.553 0.432.50 1.589 1.590 0.06 1.632 1.635 0.193.00 1.667 1.673 0.37 1.706 1.717 0.653.50 1.735 1.742 0.43 1.771 1.780 0.474.00 1.795 1.805 0.54 1.830 1.842 0.664.50 1.851 1.860 0.50 1.883 1.894 0.585.00 1.901 1.911 0.55 1.932 1.946 0.736.00 1.990 2.002 0.59 2.019 2.023 0.227.00 2.069 2.081 0.60 2.095 2.101 0.278.00 2.138 2.152 0.64 2.163 2.178 0.699.00 2.201 2.213 0.54 2.224 2.236 0.5310.0 2.258 2.270 0.53 2.280 2.294 0.6212.0 2.357 2.370 0.56 2.377 2.393 0.6614.0 2.441 2.457 0.68 2.459 2.473 0.5516.0 2.512 2.535 0.90 2.530 2.553 0.9018.0 2.576 2.601 0.96 2.593 2.616 0.8920.0 2.634 2.662 1.08 2.650 2.679 1.09T surf
700 K 1000 KMass [M ⊕ ] Radius A [R ⊕ ] Radius Z [R ⊕ ] δ R [%] Radius A [R ⊕ ] Radius Z [R ⊕ ] δ R [%]0.50 1.219 1.232 1.04 1.387 1.397 0.731.00 1.384 1.392 0.57 1.498 1.511 0.861.50 1.502 1.512 0.64 1.594 1.612 1.102.00 1.597 1.609 0.73 1.676 1.696 1.182.50 1.678 1.686 0.47 1.748 1.764 0.933.00 1.748 1.762 0.82 1.811 1.832 1.133.50 1.810 1.822 0.64 1.869 1.887 0.974.00 1.866 1.881 0.81 1.921 1.942 1.084.50 1.917 1.931 0.72 1.969 1.988 0.965.00 1.964 1.981 0.85 2.013 2.034 1.026.00 2.049 2.056 0.34 2.093 2.105 0.567.00 2.123 2.130 0.36 2.164 2.176 0.568.00 2.189 2.205 0.74 2.227 2.247 0.889.00 2.249 2.262 0.60 2.285 2.302 0.7310.0 2.303 2.319 0.70 2.338 2.356 0.7912.0 2.398 2.415 0.70 2.430 2.448 0.7614.0 2.479 2.493 0.57 2.508 2.524 0.6316.0 2.549 2.571 0.88 2.576 2.600 0.9418.0 2.611 2.634 0.87 2.636 2.660 0.9220.0 2.666 2.696 1.12 2.691 2.721 1.12 Article number, page 17 of 20 & A proofs: manuscript no. waterpaper T a b l e B . . AQUA - e qu a ti ono f s t a t e f o r w a t e r , a s a f un c ti ono f p r e ss u r ea nd t e m p e r a t u r e . T h ec o m p l e t e t a b l e i s a v a il a b l e i n e l ec t r on i c f o r m a tt h e C D S v i aa nony m ou s f t p t o c d s a r c . u - s t r a s bg . fr( . . . ) o r v i a http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/ . I t ca n a l s ob e do w n l o a d e d fr o m https://github.com/mnijh/AQUA . T h ec o l u m n s a r e p r e ss u r e P , t e m p e r a t u r e T , d e n s it y ρ , a d i a b a ti c t e m p e r a t u r e g r a d i e n t ∇ A d , s p ec i fi ce n t r opy S , s p ec i fi c i n t e r n a l e n e r gy U , bu l k s p ee do f s ound w , m ea n m o l ec u l a r w e i gh t µ , i on i s a ti on fr ac ti on X i on , d i ss o c i a ti on fr ac ti on X d a nd t h e ph a s e i d e n ti fi e r . P [ P a ] T [ K ] ρ [ kg / m ] ∇ A d S [ J / ( kg · K )] U [ J / kg ] w [ m / s ] µ [ kg / m o l ] X i on X d P h a s e I D . E - . E + . E + . E - . E + . E + . E + . E - . . - . E - . E + . E + . E - . E + . E + . E + . E - . . - . E - . E + . E + . E - . E + . E + . E + . E - . . - . E - . E + . E + . E - . E + . E + . E + . E - . . - . E - . E + . E + . E - . E + . E + . E + . E - . . - . E - . E + . E + . E - . E + . E + . E + . E - . . - . E - . E + . E + . E - . E + . E + . E + . E - . . - . E - . E + . E + . E - . E + . E + . E + . E - . . - . E - . E + . E + . E - . E + . E + . E + . E - . . - . E - . E + . E + . E - . E + . E + . E + . E - . . - . E - . E + . E + . E - . E + . E + . E + . E - . . - . E - . E + . E + . E - . E + . E + . E + . E - . . - . E - . E + . E + . E - . E + . E + . E + . E - . . - . E - . E + . E + . E - . E + . E + . E + . E - . . - . E - . E + . E + . E - . E + . E + . E + . E - . . - . E - . E + . E + . E - . E + . E + . E + . E - . . - . E - . E + . E + . E - . E + . E + . E + . E - . . - . E - . E + . E + . E - . E + . E + . E + . E - . . - . E - . E + . E + . E - . E + . E + . E + . E - . . - . E - . E + . E + . E - . E + . E + . E + . E - . . - . E - . E + . E + . E - . E + . E + . E + . E - . . - Article number, page 18 of 20onas Haldemann et al.: AQUA: A Collection of H O Equations of State T a b l e B . . AQUA - e qu a ti ono f s t a t e f o r w a t e r , t a bu l a t e d a s a f un c ti ono f d e n s it y a nd t e m p e r a t u r e . T h ec o m p l e t e t a b l e i s a v a il a b l e i n e l ec t r on i c f o r m a tt h e C D S v i aa nony m ou s f t p t o c d s a r c . u - s t r a s bg . fr( . . . ) o r v i a http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/ . I t ca n a l s ob e do w n l o a d e d fr o m https://github.com/mnijh/AQUA . T h ec o l u m n s a r e d e n s it y ρ , t e m p e r a t u r e T , p r e ss u r e P , a d i a b a ti c t e m p e r a t u r e g r a d i e n t ∇ A d , s p ec i fi ce n t r opy S , s p ec i fi c i n t e r n a l e n e r gy U , bu l k s p ee do f s ound w , m ea n m o l ec u l a r w e i gh t µ , i on i s a ti on fr ac ti on X i on , d i ss o c i a ti on fr ac ti on X d a nd t h e ph a s e i d e n ti fi e r . ρ [ kg / m ] T [ K ] P [ P a ] ∇ A d S [ J / ( kg · K )] U [ J / kg ] w [ m / s ] µ [ kg / m o l ] X i on X d P h a s e I D . E - . E + . E - . E - . E + . E + . E + . E - . .
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03 1 . E - . E + . E - . E - . E + . E + . E + . E - . . Article number, page 19 of 20 & A proofs: manuscript no. waterpaper T a b l e B . . AQUA - e qu a ti ono f s t a t e f o r w a t e r , t a bu l a t e d a s a f un c ti ono f d e n s it y a nd i n t e r n a l e n e r gy . T h ec o m p l e t e t a b l e i s a v a il a b l e i n e l ec t r on i c f o r m a tt h e C D S v i aa nony m ou s f t p t o c d s a r c . u - s t r a s bg . fr( . . . ) o r v i a http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/ . I t ca n a l s ob e do w n l o a d e d fr o m https://github.com/mnijh/AQUA . T h ec o l u m n s a r e d e n s it y ρ , s p ec i fi c i n t e r n a l e n e r gy U , p r e ss u r e P , t e m p e r a t u r e T , a d i a b a ti c t e m p e r a t u r e g r a d i e n t ∇ A d , s p ec i fi ce n t r opy S , bu l k s p ee do f s ound w , m ea n m o l ec u l a r w e i gh t µ , i on i s a ti on fr ac ti on X i on , d i ss o c i a ti on fr ac ti on X d a nd t h e ph a s e i d e n ti fi e r . ρ [ kg / m ] U [ J / kg ] P [ P a ] T [ K ] ∇ A d S [ J / ( kg · K )] w [ m / s ] µ [ kg / m o l ] X i on X d P h a s e I D . E - . E + . E + . E + . E + . E + . E + . E + . . -
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