the chemistry of extrasolar planetary systems
DESCRIPTION
The Chemistry of Extrasolar Planetary Systems. Jade Bond PhD Defense 31 st October 2008. Extrasolar Planets. First detected in 1995 313 known planets inc. 5 “super-Earths” Host stars appear metal-rich, esp. Fe Similar trends in Mg, Si, Al. Santos et al. (2003). Neutron Capture Elements. - PowerPoint PPT PresentationTRANSCRIPT
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The Chemistry of Extrasolar Planetary
Systems
Jade BondPhD Defense
31st October 2008
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Extrasolar Planets• First detected in 1995
• 313 known planets inc. 5 “super-Earths”
• Host stars appear metal-rich, esp. Fe
• Similar trends in Mg, Si, Al
Santos et al. (2003)
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Neutron Capture Elements
• Look beyond the “Iron peak” and consider r- and s-process elements
• Specific formation environments
• r-process: supernovae
• s-process: AGB stars, He burning
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Neutron Capture Elements
• 118 F and G type stars (28 hosts) from the Anglo-Australian Planet Search
• Y, Zr, Ba (s-process) Eu (r-process) and Nd (mix)
• Mg, O, Cr to complement previous work
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-0.50
0.00
0.50
-0.50 0.00 0.50
[ Fe/H ]
[ E
u/H
]
-0.50
0.00
0.50
-0.50 0.00 0.50
[ Fe/H ]
[ Y
/H ]
Host Star EnrichmentMean [Y/H]
Host: -0.05 + 0.03Non-Host: -0.16 + 0.01
Mean [Eu/H]Host: -0.10 + 0.03
Non-Host: -0.16 + 0.02
[Y/H] SlopeHost: 0.87
Non-Host: 0.78
[Eu/H] SlopeHost: 0.56
Non-Host: 0.48
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Host Star Enrichment
• Host stars enriched over non-host stars
• Elemental abundances are in keeping with galactic evolutionary trends
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Host Star Enrichment
0.00
5.00
10.00
-0.50 -0.40 -0.30 -0.20 -0.10 0.00 0.10 0.20 0.30
[ Y/H ]
M s
ini (
M Ju
p)
0.00
1.00
2.00
3.00
4.00
5.00
-0.50 -0.40 -0.30 -0.20 -0.10 0.00 0.10 0.20 0.30
[ Y/H ]
a (A
U)
0.00
0.50
1.00
-0.50 -0.40 -0.30 -0.20 -0.10 0.00 0.10 0.20 0.30
[ Y/H ]
e
0
1000
2000
3000
4000
-0.50 -0.40 -0.30 -0.20 -0.10 0.00 0.10 0.20 0.30
[ Y/H ]
Per
iod
(day
s)
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Host Star Enrichment
• No correlation with planetary parameters
• Enrichment is PRIMORDIAL not photospheric pollution
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Two Big Questions
1. Are terrestrial planets likely to exist in known extrasolar planetary
systems?
2. What would they be like?
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?
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Chemistry meets Dynamics
• Most dynamical studies of planetesimal formation have neglected chemical constraints
• Most chemical studies of planetesimal formation have neglected specific dynamical studies
• This issue has become more pronounced with studies of extrasolar planetary systems which are both dynamically and chemically unusual
• Astrobiologically significant
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Chemistry meets Dynamics
• Combine dynamical models of terrestrial planet formation with chemical equilibrium models of the condensation of solids in the protoplanetary nebulae
• Determine if terrestrial planets are likely to form and their bulk elemental abundances
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Dynamical simulations reproduce the terrestrial
planets• Use very high resolution n-body accretion
simulations of terrestrial planet accretion (e.g. O’Brien et al. 2006)
• Start with 25 Mars mass embryos and ~1000 planetesimals from 0.3 AU to 4 AU
• Incorporate dynamical friction
• Neglects mass loss
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Equilibrium thermodynamics predict bulk compositions of
planetesimals
Davis (2006)
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Equilibrium thermodynamics predict bulk compositions of
planetesimals• Consider 16 elements: H, He, C, N, O, Na, Mg, Al, Si,
P, S, Ca, Ti, Cr, Fe, Ni
• Assign each embryo and planetesimal a composition based on formation region
• Adopt the P-T profiles of Hersant et al (2001) at 7 time steps (0.25 – 3 Myr)
• Assume no volatile loss during accretion, homogeneity and equilibrium is maintained
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“Ground Truthing”
• Consider a Solar System simulation:– 1.15 MEarth at 0.64AU
– 0.81 MEarth at 1.21AU
– 0.78 MEarth at 1.69AU
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Results
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Results
• Reasonable agreement with planetary abundances– Values are within 1 wt%, except for Mg, O, Fe and S
• Normalized deviations:– Na (up to 4x)– S (up to 3.5x)
• Water rich (CJS)
• Geochemical ratios between Earth and Mars
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Extrasolar “Earths”• Apply same methodology to extrasolar systems
• Use spectroscopic photospheric abundances (H, He, C, N, O, Na, Mg, Al, Si, P, S, Ca, Ti, Cr, Fe, Ni)
• Compositions determined by equilibrium
• Embryos from 0.3 AU to innermost giant planet
• No planetesimals
• Assumed closed systems
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Assumptions
• In-situ formation (dynamics)
• Inner region formation (dynamics)
• Snapshot approach (chemistry)
• Sensitive to the timing of condensation and equilibration (chemistry)
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Extrasolar “Earths”• Terrestrial planets formed in ALL systems
studied
• Most <1 Earth-mass within 2AU of the host star
• Often multiple terrestrial planets formed
• Low degrees of radial mixing
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Extrasolar “Earths”• Examine four ESP systems
• Gl777A – 1.04 MSUN G star, [Fe/H] = 0.24• 0.06 MJ planet at 0.13AU• 1.50 MJ planet at 3.92AU
• HD72659 – 0.95 MSUN G star, [Fe/H] = -0.14• 3.30 MJ planet at 4.16AU
• HD19994 1.35 MSUN F star, [Fe/H] = 0.23• 1.69 MJ at 1.43AU
• HD4203 – 1.06 MSUN G star, [Fe/H] = 0.22• 2.10 MJ planet at 1.09AU
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Gl777A
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Gl777A1.10 MEarth at 0.89AU
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HD72659
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HD726591.35 MEarth at 0.89AU
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HD72659
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HD726591.53 MEarth at 0.38AU
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Semimajor Axis (AU)
0.0 0.2 0.4 0.6 0.8 1.0
O
Fe
Mg
Si
C
S
Al
Ca
Other
HD72659
1.53 MEarth 1.35 MEarth
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HD19994
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HD199940.62 MEarth at 0.37AU
7 wt% C
45 wt%
16 wt% 32 wt%
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HD4203
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HD42030.17 MEarth at 0.28AU
53 wt% 43 wt%
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Two Classes
• Earth-like & refractory compositions (Gl777A, HD72659)
• C-rich compositions (HD19994, HD4203)
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Mg/Si
0.5 1.0 1.5 2.0
C/O
0.0
0.5
1.0
1.5
MgSiO3 + Mg2SiO4
MgSiO3 +
SiO2 species
SiO
SiC
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Mg/Si
0.5 1.0 1.5 2.0
C/O
0.0
0.5
1.0
1.5
Solar
MgSiO3 + Mg2SiO4
MgSiO3 +
SiO2 species
SiO
SiC
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Mg/Si
0.5 1.0 1.5 2.0
C/O
0.0
0.5
1.0
1.5
Solar
HD19994
MgSiO3 + Mg2SiO4
HD72659MgSiO3 +
SiO2 species
SiO
SiC
HD4203
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Terrestrial Planets are likely in most ESP systems
• Terrestrial planets are common• Geology of these planets may be unlike
anything we see in the Solar System– Earth-like planets– Carbon as major rock-forming mineral
• Implications for plate tectonics, interior structure, surface features, atmospheric compositions, planetary detection . . .
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Water and Habitability
• All planets form “dry”• Exogenous delivery and adsorption
limited in C-rich systems – Hydrous species– Water vapor restricted
• 6 Earth-like planets produced in habitable zone
• Ideal targets for future surveys
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Take-Home Message
• Extrasolar planetary systems are enriched but with normal evolutions
• Dynamical models predict that terrestrial planets are common
• Two main types of planets:1. Earth-like2. C-rich
• Wide variety of planetary implications
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Frank Zappa
There is more stupidity than hydrogen in the universe, and it has
a longer shelf life.
Frank Zappa
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Questions?
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Just in case . . .
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Mars fractionation line
Al/Si (weight ratio)
0.00 0.05 0.10 0.15 0.20
Mg
/Si (
wei
gh
t ra
tio
)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4Earth fractionation line
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Hersant Model
• P gradient– 1/ρ(dP/dz) = -Ω2z – 4πGΣ
• Heat flux gradient– dF/dz = (9/4) ρΩ
• T gradient– dT/dz = -T/
• Surface density gradient– d Σ /dz = ρ