Planetesimal Compositions in Exoplanet Systems Torrence V. Johnson1, J. I. Lunine2, and O. Mousis3 (1)Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA, 91109, USA; (2) Dipartimento di Fisica, Università degli Studi di Roma "Tor Vergata", 00133 Rome, Italy (3) Institut UTINAM, CNRS-UMR 6213, Observatoire de Besançon, Besançon, France. 1. The Solar System Fig. 2 Planetesimal Composition

Stellar Nebula Condensates: Oxidizing, CO - rich Warm Nebula - Oxidizing Cool Nebula - Oxidizing HD19994 In our solar system, the composition of planetesimals formed beyond NH3 CO2 1% H2S CH3OH NH3 HD19994 CO2 PH3 6% N2 1% the ‘snow line’ is believed to depend strongly on the abundances of C 1% 1% H2S PH3 5% 3% 0% Silicate+Metal CO N2 1% 0% CH4 0% 0% Silicate+Metal H2O 0% CH3OH and O in the solar nebula, the redox state of C (i.e. CO rich vs. CH STAR C/O H2O CO CH4 4 1% 15% Silicate+Metal 0.80 CH4 CH3OH 39% Silicate+Metal rich regions), and the amount of carbon in the form of solid organics. H2O CH3OH CH4 CO 53% 0% 0.70 0.32 38% CO H2O CO2 35% These factors largely determine the fraction of rock plus metal, f(r–m), (a) CO2 N2 N2 NH3 0.60 Gonzales et al; Takeda et al. H2S versus volatile ice in condensates, and therefore the material NH3 Sun PH3 H2S (uncompressed) density of the condensates [1]. 0.50 C/O Uncertainty 51 Peg Gonzales 0.40 51 Peg Takeda NH3 wasp 12 NH3 N2 HD177830 CH3OH HD177830 0% CO 1% For “warm” nebula models where mid-plane temperatures are >~50K, Rock + Fraction Metal Bond et al 2010 0% H2S 1% PH3 H2S 0.30 0% CO2N2 1% CO2 PH3 Linear (Gonzales et al; Takeda et al.) 0% 1% STAR C/O CH4 8% 0% Silicate+Metal 7% 0% Silicate+Metal CO and CH4 remain in the gaseous state and water ice (and some 0% H2O H2O 0.20 CH3OH CH4 CO Silicate+Metal CH4 Silicate+Metal 1% 18% 30% hydrates) is the primary condensed volatile ice. In the outer solar 42% CH3OH CH3OH 0.10 C/O ratio = 0.8 0.35 H2O CO CO CH4 nebula, CO is expected to be the dominant C-bearing gas, resulting in 48% CO2 H2O CO2 0% 42% N2 0.00 N2 NH3 less O available to form water ice, and therefore higher values of f(r- NH3 H2S H2S m). In warmer circumplanetary environments with higher density, [C/O ] dex, Sun =0 PH3 kinetic considerations are expected to produce more reducing conditions, with CH4 being the primary carbon species [2], resulting in NH3 NH3 HD213240 HD213240 0% CH3OH 0% more water ice and lower values of f(r-m). In “cool” nebula models, N2 H2S 2% CO2 H2S PH3 N2 PH3 STAR C/O CO 0% CO2 1% 11% 1% 0% Silicate+Metal 2% 0% Silicate+Metal CH4 0% 11% with lower mid-plane temperatures, more volatile ices and clathrates, H2O H2O Stellar Nebula Condensates: Reducing, CH4 -rich 0% H2O CH4 CH4 1.00 11% including CO, CH4 and, H2S, are added to the water ice and f(r-m) is (b) CH3OH CO Silicate+Metal CH3OH 0.51 48% Silicate+Metal CO 25% CO 75% lower. 0.90 CO2 H2O CO2 N2 11% N2 NH3 0.80 NH3 CH3OH H2S 2% CH4 H2S 0% PH3 2. Exoplanet Systems 0.70

0.60 Gonzales et al.; Takeda et al. Exoplanet host stars have observed metallicities that cluster around Sun 0.50 C/O Uncertainty NH3 Sun Sun 1% H2S 51 Peg Gonzales CH3OH N2 PH3 the solar value or higher. However, the detailed compositions for ma- 0% 2% Silicate+Metal NH3 H2S 51 Peg Takeda 2% CO 0% N2 PH3 Silicate+Metal 0.40 CO2 1% 2% STAR C/O 0% H2O 3% 0% jor planet forming elements are observed to differ significantly. wasp 12 CH4 CO2 11% H2O 0% 12% CH4 CH4

Fraction Rock + Fraction Metal Bond et al 2010 H2O 0.30 CH3OH Silicate+Metal CH3OH Linear (Gonzales et al.; Takeda et al.) 18% Assuming this reflects equivalent differences in the protoplanetary Silicate+Metal 39% CO CO CO 0.55 65% 25% 0.20 CO2 CO2 H2O nebulae from which planets formed in these systems, we can estimate N2 N2 17% NH3 NH3 0.10 the range of possible f(r-m) in systems for which stellar composition C/O ratio = 0.8 H2S H2S CH3OH CH4 PH3 PH3 2% 0% data are available (the most important solid forming elements being C, 0.00 O, Si, S, Fe and Ni for these purposes). Stellar data are from two ‐0.3 ‐0.2 ‐0.1 0 0.1 0.2 0.3 0.4 0.5 [C/O ] dex, Sun =0 Gl777A surveys [3, 4], with a total of 25 exoplanet host stars, and ten stars H2S Gl777A N2 NH3 2% CO H2S PH3 0% 2% 0% NH3 2% PH3 0% Silicate+Metal compiled for a study of diversity in extrasolar terrestrial planets [5]. N2 0% STAR C/O CH3OH 0% Silicate+Metal H2O 0% CO2 Figure 1 Rock-metal fraction f(r-m) vs C/O. [C/O] is expressed as logarithmic 3% H2O CO2 15% CH4 Also, an example of a host star of a transiting planet, WASP-12 was Silicate+Metal CH4 17% CH4 CH3OH units, dex, relative to the Sun = 0, [C/O] = log (C/O)star –log(C/O)Sun.(a) 40% 0% CH3OH CO included [6]. We calculated f(r-m) for these compositions, assuming 0.63 H2O CO Oxidizing: All carbon in gaseous phase as CO (b) Reducing: All carbon in Silicate+Metal CO CO2 5% 73% 33% water is the only condensed volatile, following the solar composition CO2 N2 gaseous phase as CH4. Solar values are from Asplund et al. (2009) [8]. N2 NH3 NH3 H2O H2S scheme developed in [1,7]. As expected, the condensate rock plus CH4 5% PH3 H2S CH3OH 0% metal fraction is generally correlated with metallicity, [Fe/H]. However, 4. Summary 3% it is even more strongly influenced by the C/O ratio. Figure 1 shows f(r- • Exoplanet systems around stars with different compositions from the HD72659 m) vs. [C/O], in dex with Sun=0, for both the oxidizing and reducing NH3 Sun may have planetesimals formed beyond the ‘’snow line’’ which HD72659 H2S NH3 N2 0% PH3 CO N2 H2S 1% 0% 2% 0% Silicate+Metal nebula cases. Note that for C/O > ~0.8 both cases become ‘oxygen’ STAR C/O 0% 0% 1% PH3 have a greater range of rock and metal, carbon and ice proportions 0% Silicate+Metal H2O CH3OH CO2 CO2 H2O CH4 starved, with little or no water ice for the most carbon-rich stars. 4% 17% Silicate+Metal than solar system planetesimals. 20% CH4 35% CH3OH CH4 0.68 CH3OH CO 0% • The fraction of rock plus metal in extrasolar planetesimals is most Silicate+Metal CO CO CO2 H2O 70% 38% CO2 N2 The total range of f(r-m) possible in these systems is 5% strongly dependent on the C/O ratio in their stellar nebula rather than N2 NH3 H2O NH3 CH4 4% H2S considerably greater than the solar case (~ 0.47-0.76). 0% metallicity, [Fe/H]. H2S PH3 CH3OH • These characteristics may be investigated for extrasolar systems in 3% 3. Composition of Planetesimals vs Stellar C/O the future through their impact on the refractory and volatile content of

HD108874 extrasolar planetesimal belts and the amount of heavy element HD108874 NH3 0% H2S H2S NH3 PH3 To explore the range of planetesimal composition as function of the 2% PH3 N2 1% enrichment of extrasolar giant planets (e.g. Mousis et al. 2009, [9]). CO 0% 0% Silicate+Metal 0% Silicate+Metal 2% STAR C/O 0%N2 0% H2O C/O ratio of the host star, we combined the f(r-m) calculation from [1] H2O CO2 CO2 CH3OH CH4 16% CH4 3% 18% Silicate+Metal CH3OH with a more complete thermodynamic treatment of the volatile ices CH3OH 41% H2O CO 0.71 CO References 0% CO Silicate+Metal CO2 [9,10,11]. We used the set of stars compiled by Bond et al. [5], 77% CO2 34% CH4 N2 [1] Wong, M. H., et al., in Oxygen in the Solar System, G. J. MacPherson, Ed. (Mineralogical Society of N2 0% NH3 covering a wide range of C/O stellar values and calculated the mass NH3 America, Chan-tilly, VA, 2008), vol. Reviews in Mineralogy and Geochemi-stry Vol. 68, pp. 241-246. H2O H2S H2S CH4 0% PH3 CH3OH 3% fraction of each condensed species for both “warm” and “cool” [2] Prinn, R. G. and B. Fegley (1981) Astrophys. J. 249, 308-317. PH3 3% nebular cases. Silicate plus metal fractions for the “warm” case are [3] Gonzales, G., et al. (2001) Astron. J. 121, 432-452. [4] Takeda, Y., et al. (2001) Publications of the Astronomi-cal Society of Japan 53, 1211-1221. Warm Nebula - Reducing Cool Nebula - Reducing similar to the values in Fig. 1, reduced by the addition of small [5] Bond, J. C., et al. (2010) Astrophys. J. 715, 1050-1070. CO CO2 N2 NH3 HD4203 CO CO2 N2 NH3 HD4203 PH3 PH3 0% 0% 0% 3% H2S [6] Fossati, L., et al. (2010) Astrophys. J. 720, 872-886. 0% 0% 0% 3% H2S 0% amounts of ices containing CO (oxidizing) and NH hydrates 0% 1% 2 3 1% CH3OH Silicate+Metal STAR C/O CH3OH Silicate+Metal [7] Johnson, T. V. and J. I. Lunine (2005) Nature 435, 69-71. 0% 0% CH4 H2O CH4 H2O (reducing). For the “cool” cases, larger amounts of CO and CH4 ices 19% CH4 [8] Asplund, M., et al. (2009) Annual Review of Astronomy and Astrophysics 47, 481-522. 19% CH4 H2O CH3OH H2O CH3OH [9] Mousis, O., et al. (2009) Astron. Astrophys. 507, 1671-1674. 11% Silicate+Metal reduce f(r-m) still further . Fig. 2 illustrates the relative proportions of 1.51 11% Silicate+Metal CO CO 66% 66% CO2 [10] Mousis, O., et al. (2011) Astrophys. J. 727:77 (7pp) CO2 the condensed phases for oxidizing conditions over a range of stellar N2 N2 [11] Mousis, O., et al. (2009) Astrophys. J. 696, 1348-1354. NH3 NH3 C/O. Note that for the extreme carbon-rich star HD 4203, lack of O H2S H2S produces a shift to reducing conditions. Acknowledgements. TVJ’s work has been conducted at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. Government sponsorship acknowledged.