The Chemistry of Extrasolar Planetary Systems

1. The Chemistry of Extrasolar Planetary Systems J. Bond, D. O’Brien and D. Lauretta

2. Extrasolar Planets First detected in 1995 374 known planets Host stars appear metal-rich, esp. Fe Similar trends in Mg, Si, C, O, Ti, Al, Na, Mn, Co, Ni, Sc, V, Cu, Zr and Nd Santos et al. (2003)

3. Host Star Enrichment Elemental abundances are in keeping with galactic evolutionary trends No correlation with planetary parameters Enrichment is PRIMORDIAL not photospheric pollution

4. SiC SiO MgSiO3 + SiO2 Mg2SiO4 + MgO MgSiO3 + Mg2SiO4

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

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11. 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 • Combine dynamical models of extrasolar terrestrial planet formation with chemical equilibrium models of the condensation of solids in the protoplanetary nebulae

12. 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 innermost giant planet • Incorporate dynamical friction • Neglects mass loss

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

14. 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

15. “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

16. Results

17. 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 (Al/Si and Mg/Si) between Earth and Mars

18. 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) • No planetesimals • Assumed closed systems

19. Assumptions In-situ formation (dynamics) Inner region formation (dynamics) Snapshot approach; sensitive to the timing of condensation (chemistry) PRELIMINARY SIMULATIONS!

20. 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

21. Extrasolar “Earths” • HD72659 – 0.95 MSUN G star • 3.30 MJ planet at 4.16AU • Gl777A – 1.04 MSUN G star • 0.06 MJ planet at 0.13AU • 1.50 MJ planet at 3.92AU • HD108874 – 1.00 MSUN G star • 1.36 MJ planet at 1.05AU • 1.02 MJ planet at 2.68AU

22. Extrasolar “Earths”

23. HD72659

24. HD72659 1.35 MEarth at 0.89AU

25. HD72659

26. HD72659 1.53 MEarth at 0.38AU

27. HD72659 1.53 M Earth 0.38 AU 1.53 MEarth 1.35 M Earth 0.89 AU 1.35 MEarth

28. Gl777A

29. Gl 777A 0.27 wt% C 1.10 MEarth at 0.89AU

30. HD108874

31. HD108874 0.46 MEarth at 0.38AU 27 wt% C 66 wt% C

32. HD108874 0.46 MEarth at 0.38AU 66 wt% 27 wt%

33. Two Classes • Earth-like & refractory compositions (HD72659) • C-rich compositions (Gl777A, HD108874)

34. HD108874 SiC Gl777 SiO HD72659 MgSiO3 + SiO2 Mg2SiO4 + MgO MgSiO3 + Mg2SiO4

35. Implications Plate tectonics Atmospheric composition Biology Detectability

36. Habitability 10 Earth-like and 3 C-enriched planets produced in habitable zone Ideal targets for future surveys; Kepler

37. Water Worlds? All planets form “dry” Giant planet migration is likely to increase water content Exogenous delivery and adsorption limited in C-rich systems Hydrous species Water vapor restricted

38. Mass Distribution Carbide phases are refractory in nature Alternative mass distribution may be needed with high C systems

41. Mass Distribution

42. Where to next? Migration simulations Hypothetical giant planet systems M-dwarfs Difficult to obtain stellar abundances Alternative mass distributions Require detailed disk models Planetary structures and processes Equations of state for unusual compositions

43. Take-Home Message Extrasolar planetary systems are enriched but with normal evolutions Two main types of planets: Earth-like C-rich Wide variety of planetary and astrobiological implications

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