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The Diversity of Extrasolar Terrestrial Planets

The Diversity of Extrasolar Terrestrial Planets. J. Carter-Bond, D. O’Brien & C. Tinney RSAA Colloquium 12 April 2012. Stars → building blocks → terrestrial planets. In terms of extrasolar terrestrial planets, we generally consider other “Earth-like” planets

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The Diversity of Extrasolar Terrestrial Planets

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  1. The Diversity of Extrasolar Terrestrial Planets J. Carter-Bond, D. O’Brien & C. Tinney RSAA Colloquium 12 April 2012

  2. Stars → building blocks → terrestrial planets • In terms of extrasolar terrestrial planets, we generally consider other “Earth-like” planets • Metallic core, silicate mantle and crust • Atmosphere • Active on the planetary scale • BUT extrasolar planetary systems are chemically and dynamically unusual! • Since these different compositions may produce different planetary building blocks, what types of terrestrial planets may exist?

  3. How common is Earth?

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

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

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

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

  8. WARNING: SOMEWHAT CONTROVERSIAL SiC SiO MgSiO3 + SiO2 Mg2SiO4 + MgO MgSiO3 + Mg2SiO4

  9. Chemistry meets Dynamics • Most dynamical studies of planetesimal formation have neglected chemical constraints • Most chemical studies of planetesimal formation have neglected specific dynamical studies Combine dynamical models of terrestrial planet formation with chemical equilibrium models of the condensation of solids in the protoplanetary nebulae

  10. Dynamical simulations “produce” the terrestrial planets • Use very high resolution n-body accretion simulations of terrestrial planet accretion (e.g. O’Brien et al. 2006) • Incorporate dynamical friction • Start with 25 Mars mass embryos and ~1000 planetesimals from 0.3 AU to innermost giant planet • Neglects mass loss

  11. Equilibrium thermodynamics predict bulk compositions of planetesimals • Use spectroscopic photospheric abundances of 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 radial P-T profiles • Assume no volatile loss during accretion, homogeneity and equilibrium is maintained

  12. Equilibrium thermodynamics predict bulk compositions of planetesimals

  13. Extrasolar “Earths” • Terrestrial planets formed in ALL systems studied • Most <1 Earth-mass • Often multiple terrestrial planets formed

  14. Extrasolar “Earths” • Examine three ESP systems • HD72659 – 0.95 MSUN G star, [Fe/H] = -0.14 • 3.30 MJ planet at 4.16AU • Gl777A – 1.04 MSUN G star, [Fe/H] = 0.24 • 0.06 MJ planet at 0.13AU • 1.50 MJ planet at 3.92AU • HD108874 – 1.00 MSUN G star, [Fe/H] = 0.23 • 1.30 MJ planet at 1.05AU • 1.07 MJ planet at 2.75AU

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

  16. HD72659

  17. HD72659 1.03 M Earth 0.95AU C/O = 0.40

  18. Gl777

  19. Gl777 1.10 M Earth 0.89AU C/O = 0.78

  20. HD108874

  21. HD108874 0.46 M Earth 0.38AU C/O = 1.35

  22. HD72659 Gl777 HD108874 1.03 M Earth 0.95AU C/O = 0.40 1.10 M Earth 0.89AU C/O = 0.78 0.46 M Earth 0.38AU C/O = 1.35

  23. What About Migration? Giant planet migration is believed to have occurred in many extrasolar planetary systems. Migration can move a large amount material both inwards and outwards → possibly change final planet composition.

  24. Consider Three Scenarios • In-Situ formation (Jupiter-mass body doesn’t migrate from 1AU) • Jupiter-mass body migrates from 5AU to 1AU • Jupiter-mass body migrates from 5AU to 0.25AU

  25. Consider Three Compositions • Solar • Gl777 (C/O = 0.78) • HD4203 (C/O = 1.85)

  26. Solar Composition:

  27. Gl777 Composition:

  28. HD4203 Composition:

  29. Water? • Water is primarily present as water ice and serpentine • Significantly less water in high C/O systems • Less water ice • Restricted water vapor distribution

  30. Water? • Migration can deliver massive amounts of water to the “dry” inner regions of the planetary systems. • In-situ – no water delivered • Migration – water and hydrous phases delivered to inner regions, refractories delivered to outer regions

  31. Water? Example: 3.05 MEarth at 0.91AU

  32. Atmospheres • Atmospheric formation is a complex process combining capture, outgassing, loss, etc. • For close in planets with Teff> 1000K (within about 0.1AU), we can approximate an atmospheric composition by assuming equilibrium between the crust and atmosphere

  33. Atmospheres Solar Composition: 79% H2 20% H2O 1% H2S CO and CO2 with ices HD4203: 53% CO 42% H2 21% CO2 17%H2O 0.5%CH4

  34. Atmospheres Taken from Lissauer et al., 2011.

  35. Biological Elements Lacking biological elements N & P missing on all H missing on in-situ Possible alternative delivery through migration and volatiles?

  36. Biological Elements Condensates, Clathrates & Hydrates: CH3OH NH3 CO2 H2S PH3 CH4 CO N2 STAY TUNED!

  37. Terrestrial Planets are likely to be relatively common • Large range of stellar compositions suggests a wide range of terrestrial planets • Final planet compositions depend somewhat on giant planet migration history • Wide variety of biological, chemical and planetary implications

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

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