The Chemistry of Extrasolar Planetary Systems Jade Bond PhD Defense 31 st October 2008

Extrasolar Planets First detected in 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 Look beyond the “Iron peak” and consider r- and s-process elements Specific formation environments r-process: supernovae s-process: AGB stars, He burning

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

Host Star Enrichment Mean [Y/H] Host: Non-Host: Mean [Eu/H] Host: Non-Host: [Y/H] Slope Host: 0.87 Non-Host: 0.78 [Eu/H] Slope Host: 0.56 Non-Host: 0.48

Host Star Enrichment Host stars enriched over non-host stars Elemental abundances are in keeping with galactic evolutionary trends

Host Star Enrichment

No correlation with planetary parameters Enrichment is PRIMORDIAL not photospheric pollution

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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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

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

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

Equilibrium thermodynamics predict bulk compositions of planetesimals Davis (2006)

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

“Ground Truthing” Consider a Solar System simulation: –1.15 M Earth at 0.64AU –0.81 M Earth at 1.21AU –0.78 M Earth at 1.69AU

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

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

Assumptions In-situ formation (dynamics) Inner region formation (dynamics) Snapshot approach (chemistry) Sensitive to the timing of condensation and equilibration (chemistry)

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

Extrasolar “Earths” Examine four ESP systems Gl777A – 1.04 M SUN G star, [Fe/H] = M J planet at 0.13AU 1.50 M J planet at 3.92AU HD72659 – 0.95 M SUN G star, [Fe/H] = M J planet at 4.16AU HD M SUN F star, [Fe/H] = M J at 1.43AU HD4203 – 1.06 M SUN G star, [Fe/H] = M J planet at 1.09AU

Gl777A

1.10 M Earth at 0.89AU

HD72659

1.35 M Earth at 0.89AU

HD72659

1.53 M Earth at 0.38AU

HD M Earth 1.35 M Earth

HD19994

0.62 M Earth at 0.37AU 7 wt% C 45 wt% 16 wt% 32 wt%

HD4203

0.17 M Earth at 0.28AU 53 wt%43 wt%

Two Classes Earth-like & refractory compositions (Gl777A, HD72659) C-rich compositions (HD19994, HD4203)

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...

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

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-like 2.C-rich Wide variety of planetary implications

Frank Zappa There is more stupidity than hydrogen in the universe, and it has a longer shelf life. Frank Zappa

Questions?

Just in case...

Hersant Model P gradient –1/ρ(dP/dz) = -Ω 2 z – 4πGΣ Heat flux gradient –dF/dz = (9/4) ρ  Ω T gradient –dT/dz = -T  / Surface density gradient –d Σ /dz = ρ