The Diversity of Extrasolar Terrestrial Planets

J. Bond, D. Lauretta & D. O’Brien

IAU Symposium 265

14th August 2009

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

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) for 10 known extrasolar planetary systems

• Incorporate dynamical friction

• Start with Mars-mass embryos located interior to the known giant planets. All known planets are assumed to be in their current orbits

• Neglects mass loss

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 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

Solar System Testing

• “Ground tested” on Solar System simulations of O’Brien et al (2006) – good agreement

• Volatile enriched

• See Bond et al (2009) Icarus

Extrasolar “Earths”

• Terrestrial planets formed in ALL systems studied

• Most <1 Earth-mass within 2AU of the host star

• Often multiple terrestrial planets formed

• Migration may alter some of these simulations . . . stay tuned!

Extrasolar “Earths”

• 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] = 0.14• 1.36 MJ planet at 1.05AU• 1.02 MJ planet at 2.68AU

HD72659

HD72659• 1.03 MEarth at 0.95AU

Gl777A

Gl 777A• 1.10 MEarth at 0.89AU

0.27 wt% C

HD108874

HD108874• 0.46 MEarth at 0.38AU

27 wt% C66 wt% C

HD108874• 0.47 MEarth at 0.38AU

Gl777SiC

SiO

MgSiO3 + SiO2

MgSiO3 + Mg2SiO4

Mg2SiO4 + MgO

HD72659

HD108874

Terrestrial Planets may be very different in ESP systems

• Terrestrial planets may be common• Geology of these planets may be unlike

anything we see in the Solar System– Earth-like planets– Carbon as major rock-forming mineral

• Composition varies with ‘primordial’ chemical enrichments

• Implications for detection, planetary processes, atmospheric composition . . . .