The Chemistry of Extrasolar Planetary Systems

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

2. 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)

3. 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

4. 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

5. Host Star Enrichment Mean [Y/H] Host: -0.05 + 0.03 Non-Host: -0.16 + 0.01 [Y/H] Slope Host: 0.87 Non-Host: 0.78 Mean [Eu/H] Host: -0.10 + 0.03 Non-Host: -0.16 + 0.02 [Eu/H] Slope Host: 0.56 Non-Host: 0.48

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

7. Host Star Enrichment

8. Host Star Enrichment No correlation with planetary parameters Enrichment is PRIMORDIAL not photospheric pollution

9. Two Big Questions • Are terrestrial planets likely to exist in known extrasolar planetary systems? • What would they be like?

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15. 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

16. 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

17. 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

18. Equilibrium thermodynamics predict bulk compositions of planetesimals Davis (2006)

19. 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

20. “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

21. Results

22. 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

23. 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

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

25. 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

27. 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 • HD199941.35 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

28. Gl777A

29. Gl777A 1.10 MEarth at 0.89AU

30. HD72659

31. HD72659 1.35 MEarth at 0.89AU

32. HD72659

33. HD72659 1.53 MEarth at 0.38AU

34. HD72659 1.53 MEarth 1.35 MEarth

35. HD19994

36. HD19994 0.62 MEarth at 0.37AU 7 wt% C 16 wt% 32 wt% 45 wt%

37. HD4203

38. HD4203 0.17 MEarth at 0.28AU 53 wt% 43 wt%

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

44. 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 . . .

45. 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

46. 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: Earth-like C-rich Wide variety of planetary implications

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

48. Questions?

49. Just in case . . .