Download The Effect of Abundance Ratios on Rocky Planet Structure

The Effect of Abundance Ratios on
Rocky Planet Structure
Wendy Panero
Ohio State University
The Effect of Abundance Ratios on
Rocky Planet Structure
Wendy Panero
Ohio State University
JNKMA
JB 5
5AAC=I
Earth Structure
Two Major
Divisions:
*The silicate
Earth: The crust
and mantle are
composed of
silicate ceramics.
*The core:
Primarily iron,
with some Ni and
“light” elements
Hidden from
direct sampling.
Composition of the (Silicate) Earth
1
Silicate Earth/Chondrite
Mg Ca Ti REE
Si
Sc Al Zr
V
Li
Cr
Na
Mn
K
Fe
W
Rb
Co
Cu
Ni
Identical to Chondrites
F
Zn
0.1
In
Cd
Hg
Tl
0.01
Pb
Bi
Ag
Cl
Mo
As
Br
Au
C
0.001
0
Pd Rh Pt Ru Ir
Re Os
S Se Te
500
1000
1500
50% Condensation Temperature (T)
2000
Earth Structure
*The silicate
Earth:
Solid convective
motions in the
mantle give rise to
melting at the
surface, sinking of
dense oceanic
crust creating
plate tectonics.
Earth Mantle Dynamics &
Surface Plate Tectonics
3.8
3.6
Basalt-Eclogite transition
3
Density (g/cm )
Earth Composition
3.4
3.2
3.0
Mantle Density
Basalt Density (5% mantle melt)
2.8
0
2
4
6
8
Pressure (GPa)
Kelloggetetal.,
al.,1999
1999
Kellogg
Earth Mantle Dynamics
gρ 2α HD 5
Ra =
ηκ k
H radiogenic heat production
η  Viscosity (fxn composition, T)
D Layer thickness
Mantle Concentrations of
radioactive isotopes
238U
235U
232Th
40K
20 ppb
1 ppb
100 ppb
280 ppm
Kellogg et al., 1999
Planetary Dynamics from
Interior Heat Production
K
U
Th
total
Compositional variation in
exoplanet hosts
7
6
Known planet hosts
5
4
uncertainty
NAl/NSi
3
2
SUN
0.1
9
8
7
6
5
4
5
6
7
8
9
1
2
NMg/NSi
Data from
Adibekyan et al., 2012
Trace Element Variation?
Thorium variation in Solar Analogues
With known
planets
Without
known planets
Unterborn, Johnson, Panero in review
Thorium
variation
in
Solar
Analogues
4
Figure 2. Stars with observed planets are shown as closed squares and without as un
of Th as a function of Fe. The solid line represents*Factor
the bestoffit~3
to those stars belo
Unterborn,
Johnson, Panero
in review Abundance of Th as a function
relationship.
Center:
of average
variation
in Si
Thabundance
content adop
abundance. For each plot stars with observed planets are shown as closed squares a
Thorium variation in Solar Analogues
closed squares and without as unfilled squares. The Sun is shown for reference as a triangle. Left: Abunda
of ~3 represents a one-to
ts the best fit to those stars belonging to the high Fe, high Th group*Factor
and the dashed
on of average Si abundance adopting the same legend as in Th vs Fe.variation
Right: Th/Si
function of averag
in as
Tha content
ts are shown as closed squares and without as unfilled squares. The Sun is shown for reference as a triang
Unterborn, Johnson, Panero in review
Thorium variation in Terrestrial Planets
K
U
Th
total
Internal Heat Production
Potential Range
Earth
!
Thorium variation in Terrestrial Planets
Unterborn, Johnson, Panero in review
Compositional variation in exoplanet
hosts: Major Element Variation
7
6
Known planet hosts
5
4
uncertainty
NAl/NSi
3
2
SUN
0.1
9
8
7
6
5
4
5
6
7
8
9
1
NMg/NSi
2
Data from
Adibekyan et al., 2012
Mantle Mineral Primer
Olivine + polymorphs β-ol, γ-ol (aka Wadsleyite and Ringwoodite)
(Mg,Fe)SiO4
Holds water (1-2 wt% H2O)
Breaks down to bridgmanite and ferropericlase ~25 GPa
Bridgmanite
(Mg,Fe)SiO3
Stable > 25 GPa (aka Mg-Si perovskite)
Doesn’t hold water. Stiff.
Ferropericlase (aka magnesiowüstite)
(Mg,Fe)O
Doesn’t hold water. Weak.
Garnet (aka majorite, pyrope, almandine, spessartine, andradite, grossular, uvarite)
A3B2Si3O12
Holds a little water.
Breaks down to bridgmanite ~30 GPa
Earth Mantle Mineralogy
1.0
fp
Earth
Phase Fraction (%)
0.8
α-ol
0.6
β-ol
γ-ol
pv
br 0.4
0.2
gt
opx
cpx
0.0
cpv
5
10
15
20
25
30
35
Pressure (GPa)
Calculated mineralogy for pyrolitic MgO, FeO, SiO2, CaO, Al2O3, Na2O
system along a 1600 K adiabat using HeFESTo (Stixrude and Lithgow-Bertelloni 2007)
Water capacity ~10x Earth surface oceans, mostly in olivine
MgO likely changes its structure from B1 to B2 at (0.5 TPa.
wever, in the previous work by Karato (1989), creep strength
materials with B2 structure was not considered. Here, I examine
differences in high-temperature creep behavior in materials
h these two structures. Two different data sets are available
ompare the difference in viscosity between B1 and B2 struce. First is a comparison of high-temperature power-law creep
avior between NaCl (Franssen,
1994)
2
5 and CsCl (Heard and
by, 1981) (Fig. 6a). Compared at the same normalized conditions,
l shows substantially smaller creep strength than NaCl (by a fac-
Earth Mantle Dynamics
H radiogenic heat production
η  Viscosity (fxn composition, T)
D Layer thickness
gρ α HD
Ra =
ηκ k
T / Tm
0.9
0.8
0.7
0.6
10 -5 s-1
-3
pe
ro
vs
ki
σ/µ
te
10
sp
in
el
ga
ol
rn
iv
et
in
e
10 -2
10
ro
-4
10
me
lt
sa
k
c
s
tal
-5
1.1
1.2
1.3
1.4
1.5
1.6
1.7
Tm / T
Karato, 2011
5. The crystal structure versus creep strength systematics for various materials
power-law dislocation creep (based on Frost and Ashby (1982) and Karato
9)). Normalized stress (r/l, r: deviatoric stress, l: shear modulus) is plotted
nst normalized temperature (Tm/T, T: temperature, Tm: melting temperature)
strain-rate of 10$5 s$1. The results for metals include those with fcc, bcc and
Kellogg et al., 1999
MgO likely changes its structure from B1 to B2 at (0.5 TPa.
wever, in the previous work by Karato (1989), creep strength
materials with B2 structure was not considered. Here, I examine
differences in high-temperature creep behavior in materials
h these two structures. Two different data sets are available
ompare the difference in viscosity between B1 and B2 struce. First is a comparison of high-temperature power-law creep
avior between NaCl (Franssen,
1994)
2
5 and CsCl (Heard and
by, 1981) (Fig. 6a). Compared at the same normalized conditions,
l shows substantially smaller creep strength than NaCl (by a fac-
Earth Mantle Dynamics
H radiogenic heat production
η  Viscosity (fxn composition, T)
D Layer thickness
gρ HD
Ra =
ηα k
T / Tm
0.9
0.8
0.7
0.6
10 -5 s-1
-3
pe
ro
vs
ki
σ/µ
te
10
sp
in
el
ga
ol
rn
iv
et
in
e
10 -2
10
ro
-4
10
me
lt
sa
k
c
s
tal
-5
1.1
1.2
1.3
1.4
1.5
1.6
1.7
Tm / T
Karato, 2011
5. The crystal structure versus creep strength systematics for various materials
power-law dislocation creep (based on Frost and Ashby (1982) and Karato
9)). Normalized stress (r/l, r: deviatoric stress, l: shear modulus) is plotted
nst normalized temperature (Tm/T, T: temperature, Tm: melting temperature)
strain-rate of 10$5 s$1. The results for metals include those with fcc, bcc and
Kellogg et al., 1999
Mantle Mineral Primer
“Wet”
Dry
Weak
Strong
Composition Controls Water Storage
1.0
(Si/Mg)=0.4(Si/Mg)Earth
Phase Fraction
0.8
fp
0.6
α−Ol
β−Ol
γ−Ol
cf
0.4
br
0.2
0.0
gt
cpv
5
10
15
20
25
30
35
Pressure (GPa)
Dominated by ferropericlase; ~1 ocean of water capacity
Very weak mantle throughout
Composition Controls Water Storage
1.0
(Si/Mg)=2.0(Si/Mg)Earth
Phase Fraction (%)
0.8
c2c
br
0.6
opx
gt
0.4
0.2
cpx
SiO2-stishovite
0.0
5
10
15
20
25
30
35
Pressure (GPa)
No olivine or ferropericlase; ~0.1 ocean of water capacity
Very stiff mantle throughout
Compositional Impact on Plate Tectonics
3.8
3.6
Basalt-Eclogite transition
3
Density (g/cm )
Earth Composition
3.4
(Si/Mg)=1.6(Si/Mg)Earth
3.2
3.0
Mantle Density
"Basalt" Density (5% mantle melt)
2.8
0
2
4
Pressure (GPa)
6
8