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3. Interior models for w a t e r planets [4], with water oceans with NH3 neglect effects of dissolved species (salts).
5MC
Interior Structure And Habitability Of Super-Europas And Super-Ganymedes Steve Vance1,2*, R. Barnes4, J. Michael Brown2, Olivier Bollengier2, Baptiste Journaux3, Christophe Sotin1, and Mathieu Choukroun1. *[email protected] 1Jet Propulsion Laboratory, California Institute of Technology 2Department of Earth and Space Sciences, University of Washington, Seattle 3Laboratoire de Glaciologie et Géophysique de l’Environnement, Université Joseph Fourier, Grenoble, France 4Department of Astronomy, University of Washington, Seattle
A warm Ganymede with a 10 Wt% MgSO4(aq) ocean could cause ice VI to float above the seafloor interface, Other high pressure phases can also float [6].
4. Watery exoplanets will resemble larger icy satellites in the solar system, with high-pressure ices and salty oceans. !Application of detailed thermodynamics to icy satellites [5,6] reveals strong density and temperature gradients. How do deep salty oceans affect geodynamic evolution?
liquid ocean layers, more saline with depth
1100 km
800 kmIce I
Ice VIce VI
Ice III
Ganymede
700 km
possible water-rock interaction
800 km
Ice I
Ice VIce VI
Ice II-III
3000 km
Ice VII
Super Europas
5800 km
Titan
1880 km
~0 km
700 km
Ice I
Ice VIce VI
Ice II
Ice snowing upward?
~200 kmIce I
Ice III
Europa
1350km
NH3?
break-through to space or atmosphere (plumes)?
Current Region of Study
Region of Study for Fluids in Super Europas
T (oC)-100 0 100 200
P (G
Pa)
10-1
100
101
Earth
Europa
Terrestrial“Habitable Zone”
Ganymede Earth 0.4
Earth0.025
Ganymede
Kepler 11b
2.0 Kepler 18b 63
R/R M/M
1.8model values: Zeng and Sasselov 2014
10 km
100 km
800 km
300
5. Pressures in exoplanet oceans span the multi-GPa range of pressures where liquids are possible. Pressure (GPa), temperature (oC) profiles in upper mantles of selected objects [as per Ref. 7], beginning at presumed seafloor depth. !Overlying ocean assumed at a constant temperature. !Known exoplanets, albeit very hot ones, modeled as super Europas with seafloor depths like Earth’s (10 km), Europa’s (100 km, and Ganymede’s (800 km; [6]).
1. Confirmed and candidate Kepler planets with .
àWatery Earth-like planets are probably common around other stars. !
More small, cool worlds will be discovered as facilities such as TESS come into operation [1].
6. Recent EOS and phase measurements for NaCl (aq) indicate ice VII floats at P >5 GPa.
1 2 3 4900
1000
1100
1200
1300
1400
1500
1600
Pressure (GPa)
Den
sity
(kg
mï�
)
18 Wt %
6 Wt %T = 293 KT = 373 KT = 473 KT = 573 KT = 673 K
ice VI
ice VII
(1 mol kg-1)530 model planets [2]. curves separate wet (upper) and dry (lower) worlds. Jupiter’s moon Europa at the same position as the Moon.
Known exoplanets [3] of relevant size. Constant density curves (Neptune in blue and Earth in green).
R † 2.5RC
7. Modern computer processing allows us to apply geophysical methods of regularization to construct optimized “local” fits of thermodynamic properties that easily accommodate new data. !!!!!We constructed Gibbs free energies for water [13, 14, Brown et al., in prep.; left]. We are using G to develop general thermodynamics of aqueous solutions:
G = Gwater + Gex
Pressure (MPa)0 200 400 600 800 1000 1200
Tem
pera
ture
(K)
240
250
260
270
280
290
300
310
320
1.59
2.10
2.23
1.83
1.83
2.30
1.831.83
2.67
2.37
1.83
2.28
2.05
2.57
3.92
3.58
4.24
aqueoussolution
ice VI
ice V
ice IIIice II
ice Ih
2.75 m
1.75 m
2.00 m
2.25 m
2.50 m
1.25 m
1.50 m
1.00 m0.75 m0.25 m
0.50 m
1.47
0.70
solidus [Hogenboom et al., 1995]solidus [Grasset et al., 2001]solidus [Dougherty et al., 2007]new solidus datanew liquidus dataunary system equilibria [Choukroun and Grasset, 2010]binary system equilibria, thermodyamic approachbinary system equilibria, extrapolated
Gibbs free energies o f MgSO4 a l low computation of ice equilibrium under s u p e r E a r t h pressures. (Bollengier et al., in prep)
2.52
Pressure (GPa)
1.51
0.50500
400Temperature (K)
300200
0.8
0.9
1.4
1.3
1.2
1.1
1
100
Den
sity
gm
/ccDen
sity
(g/c
c)
CP “ˆB2G
BT 2
˙
P,n
⇢ “ˆBG
BP
˙´1
T,nà
Pressure (GPa)
Pitzer formulation[15]
àà
(contours: temperature in Kelvin).
3.5!! 3
0.5 0
600200
T (K) 1000 0 10 20 30
We gratefully acknowledge support from NASA’s Outer Planets Research Program. and Astrobiology Institute. A part of this work was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.
[1]Ricker, G. R., et al. (2014). SPIE Astronomical Telescopes+ Instrumentation, 914320– 914320. [2]Baraffe, I., et al. (2014). arXiv preprint arXiv:1401.4738. [3] Howe, A. R., et al. (2014). Astrophys. J., 787(2):173. [4] Fu, R., et al. (2010). Astrophys. J., 708:1326. [5] Vance S. and Brown J. M. (2013) Geochim Cosmochim Acta, 90, 1151–1154. [6] Vance S. et al. (2014) Plan. Space Sci 96, 62-70. [7] Vance et al. (2007) Astrobiology, 7, 987-1005. [8] Mantegazzi, D. et al. (2013). Geochim. Cosmochim Acta, 121:263–290. [9] Reimers, J. and Watts, R. (1984). Chem Phys, 91(2):201–223. [10] Vega, C., et al. (2005). Phys. Chem. Chem. Phys., 7(7):1450–1456. [11] Choukroun M. and Grasset O. (2010) J. Chem. Phys. 133, 144, 502. [12] Journaux, B., et al. (2013). Icarus, 226:355–363. [13] Vance S. and Brown J. M. (2010) JASA 127, 174–180. [14] Abramson, E. and Brown, J. (2004). Geochim. Cosmochim. Acta, 68(8):1827–1835 [15] Pitzer, K. (1991) CRC Press.
REFERENCES
SUMMARY •Fluid-rock interactions in super Earth oceans are regarded as limited by
negatively buoyant high pressure ices V, VI, VII, and VIII. •Analogous assumption made for large icy worlds Ganymede and Titan: ocean
depths up to 800 km create >GPa pressures (>10katm). Applying accurate fluid thermodynamics to planetary interiors challenges these assumptions.
•Increased density in highly saline oceans implies possible oceans perched under and between high pressure ices.
•In some model oceans, high-pressure ices become buoyant, implying frazil-like upward snows, interlayered liquids and fluids in direct contact with rock.
Tb:255.00 K, qb:4 mW mï2, zb:134 km
Tb:260.00 K, qb:5 mW mï2, zb:104 km
Tb:265.00 K, qb:8 mW mï2, zb:70 km
Tb:270.00 K, qb:18 mW mï2, zb:32 km
250 260 270 280 290 300 310 320 330
01002003004005006007008009001000
Temperature (K)
Dep
th (k
m)
V
VI
III
I
0 Wt % MgSO4 (aq) 10 Wt % MgSO4 (aq)
250 260 270 280 290 300 310 320 330
01002003004005006007008009001000
Temperature (K)
Dep
th (k
m)
Tb:250.00 K, qb:4 mW mï2, zb:148 km
Tb:252.50 K, qb:4 mW mï2, zb:129 km
Tb:255.00 K, qb:5 mW mï2, zb:114 km
Tb:260.00 K, qb:6 mW mï2, zb:84 km
Tb:265.00 K, qb:11 mW mï2, zb:50 km
Tb:270.00 K, qb:44 mW mï2, zb:13 km
V
VI
III
I
0 200 400 600 800 1000 1200 1400 1600 18000.95
1
1.05
1. 1
1.15
1. 2
1.25
1. 3
1.35
1. 4
1.45
Pressure (MPa)
Den
sity
(g m
Lï� )
Tb:255.00 K, qb:4 mW mï�, zb:134 km
Tb:260.00 K, qb:5 mW mï�, zb:104 km
Tb:265.00 K, qb:8 mW mï�, zb:70 km
Tb:270.00 K, qb:18 mW mï�, zb:32 km
5 wt%10 wt%15 wt %
V
VI
liquid
I
Den
sity
(g m
LD
ensi
ty (g
mï�
)
0 200 400 600 800 1000 1200 1400 1600 18000.95
1
1.05
1.1
1.15
1.2
1.25
1.3
1.35
1.4
1.45
Pressure (MPa)
Tb:250.00 K, qb:4 mW mï2, zb:148 km
Tb:252.50 K, qb:4 mW mï2, zb:129 km
Tb:255.00 K, qb:5 mW mï2, zb:114 km
Tb:260.00 K, qb:6 mW mï2, zb:84 km
Tb:265.00 K, qb:11 mW mï2, zb:50 km
Tb:270.00 K, qb:44 mW mï2, zb:13 km
5 wt%10 wt%15 wt%
III
V
VI
liquid
I
silicatesilicate
Aqueous chemistry separable by contributions from: • water (G°) • interaction of water with ions • interaction of ions with each other • interaction of ions with each other and water
Mostly unavailable and unimportant at low concentration
We are beginning to estimate Pitzer parameters under planetary conditions.
!
2. Mass-radius, planet density vs composition, etc., provide information about internal structure related to habitability. Potentially habitable super Europas are notionally in the shaded regions.
Increasing numbers
anticipated from TESS
