Volatiles: Constraints on disk evolution, and planetesimal/planets accretion Conel M. O’D. Alexander DTM, Carnegie Institution of Washington Meteorites Recorders of first few million years (Ma) Chondrites 1 cm Achondrites Irons 4,567.3±0.2 million years old Formed in <2 Ma Formed in ~2-4 Ma Chondrites – ‘cosmic’ sediments Allende (CV3) Three basic components: Chondrules, CAIs, Matrix. Lancé (CO3) ~2 cm Enstatite – EH, EL Ordinary – H, L, LL (and R) Carbonaceous – CI, CM, CR, CV, CO, CK Photomicrographs Courtesy Adrian Brearley ~2 cm Time constraints – Asteroids-Mars 0 t0=4,567 Ma (Connelly et al. 2012) ProtoJupiter = 20 M Vesta (HEDs) earth 1 Formation of angrite parent body Mars (~50%) Formation of E chondrites 2 Formation of O+R chondrites Formation of CK chondrites Formation of CV+CO chondrites 3 Time after CV CAIs(Ma) Time after Formation of CI, CM+TL chondrites 26 4 Formation of CR chondrites Al no longer an effective heat source Dissipation of the gas disk (and Grand Tack?) Time constraints - Earth t0=4,567 Myr (Connelly et al. 2012) 0 Jupiter reaches 20 Mearth? Dissipation of gas disk (and Grand Tack?) 10 Debris disk 20 30 Retention of atmosphere 40 Time after CV (Ma) CAIs Time after (Avice and Marty 2014) 50 Formation of the Moon (Touboul et al. 2007; Barboni et al. 2017) Time constraints - Earth 0 4,567 Ma (Connelly et al. 2012) Retention of atmosphere 50 (Avice and Marty, 2014) Formation of the Moon 100 (Touboul et al. 2007) 150 Evidence for oceans from oldest zircons (Wilde et al. 2001) 200 Time after Solar System formation (Ma) formation System Solar Time after What did the Earth accrete and when was it accreted? Asteroids and Comets 1100 Comets JFC 900 JFC – Jupiter Family Earth (Comets – H from H2O, OCC OCC - Oort Cloud 700 N from HCN/NH3) 500 300 N (‰) CR 15 d CM 100 TL Earth Venus -100 CI Mars -300 Solar -500 -1000 -500 0 500 1000 1500 d(‰)=(R/Rstd-1)x1000 dD (‰) R=D/H or 15N/14N Marty et al. (2016) – cometary contributions to H-C-N were minor, but may have been important for noble gases. Earth’s siderophile isotopes All inconsistent with carbonaceous chondrites Earth Earth Earth Of the carbonaceous chondrites, the CIs are closest to the Earth’s composition. Nevertheless, if CI-like material was the source of the volatiles, it must have accreted before the end of core formation – assumed to be Moon-formation. The late veneer after Moon-formation was too little and too dry. Atmosphere ≠ interior Péron et al. (2017) Mantle Ne – Solar or implanted solar wind (and H & He?) ‘Chondrite’ Either the atmosphere was not degassed from the interior, or the interior/atmosphere compositions have change after degassing? Did early planetesimals fully degas? 1100 JFC 900 Earth OCC 700 500 300 N (‰) CR 15 d CM 100 Angrite TL Earth Venus -100 Vesta CI Mars -300 Solar (Miura & Sugiura 1993; Abernethy et al. 2013; Sarafian et al. 2014,2017; Barrett et al. 2016) -500 -1000 -500 0 500 1000 1500 dD (‰) Crystallization ages Accretion ages of CIs and CMs Angrite D’Orbigny ~3.5 Ma after CAIs ~3.5 Ma after CAIs (Fujiya et al. 2013) HED Stannern ~3.6 Ma after CAIs Where did the carbonaceous chondrites form? Trouble with Saturn’s moons ISM ices Enceladus H2O Comets Earth Titan – CH4 Bulk solar Yang et al. (2013) 4000 Chondritic H is 3500 3000 a mix of H2O 2500 Organics 2000 D (‰) and organics d 1500 1000 500 0 -500 0 5 10 15 20 25 900 C/H (wt.) 700 CR 500 Tagish Lake 300 D (‰) D CR water d 100 CI Bulk Bulk -100 CM -300 CM water -500 0 2 4 6 (Alexander et al. 2012) Bulk C/H (wt.) Chondritic water was not from the outer Solar System ? 1.E-03 4000 Oort Cloud comets 3000 Enceladus RC 2000 JFC 1000 OC 0 d Earth D (‰) CR -200 1.E-04 -400 D/H Ratio D/H CM CO -600 CI Tagish Lake -800 Protosolar 1.E-05 After Alexander et al. (2012) 3Fe + 4H2O = Fe3O4 + 4H2 12000 Rayleigh fractionation 10000 O 0°C 2 8000 6000 ) of residual ) H of residual 200°C (‰ 4000 D d 2000 0 0.01 0.1 1 Fraction of H2O remaining (Alexander et al. 2010) H isotopes: Indicators of formation distance? 1.0E-03 Comets Enceladus Saturn GT Earth 1.0E-04 Titan JFCs (CH ) OCCs LL CR 4 D/H in Water in D/H CM CI Chondrites Solar 1.0E-05 0.1 1 10 100 Distance (AU) Summary • All chondrites accreted their volatiles in a ~CI-like matrix. C, N, noble gases and some H was in a macromolecular organic matter. H2O was accreted as ice that also included CO2 and HCN/NH3. No chondrite seems to have accreted their full solar H2O complement. • The initial D/H of water in CCs and non-CCs were not very different, contrary to model expectations, and less than Enceladus or even Titan. • From these perspectives, there are no compelling reasons for the CCs to have formed in outer Solar System, or at least not beyond the location of Saturn when its moons formed (3-7 AU in the Grand Tack). • CI/CM-like material was the major source of terrestrial planet H+N+C, perhaps with some solar input, but comets may have been much more important for noble gases. • Atmospheric volatiles were accreted before Moon-formation and may not have been initially stored in the Earth’s interior, yet somehow they survived impacts large and small. Roughly chondritic volatiles 1.0E-01 10-1 Cs Pb Kr Cl Cd 36Ar H 2-4% CI/CM C like material Ne 1.0E-02 10-2 I Br Late Veneer Gradual Xe loss Xe (Pujol et al. 2011)? 1.0E-03-3 BulkEarth/CI 10 Hidden N reservoir or impact loss? (Dereulle et al., 1992; Marty, 2012; Palme and O’Neill, 2014) 1.0E-0410-4 0 2 4 6 8 10 12 14 N isotopes: Indicators of formation distance? 0.008 Comet HCN/NH3 (averages) 0.007 Titan 0.006 Saturn GT N 14 0.005 Chondrites N/ (bulks) Acids Amino 15 0.004 Earth 0.003 Solar 0.002 0.1 1 10 100 Distance (AU) Strecker-cyano synthesis R-C=O + HCN + NH3 + H2O = R-CNH2-COOH ’Twin’ planets are not identical 1.0E+01 Comets or Ne Solar wind? 36Ar 1.0E+00 Kr 1.0E-01 40Ar 1.0E-02 Venus/CI Xe N C 1.0E-03 1.0E-04 1.0E-04 1.0E-03 1.0E-02 1.0E-01 1.0E+00 1.0E+01 Earth/CI Venus abundances just for atmosphere Volatiles in matrix 2.5 Bulk CV chondrites 2.0 1.5 1.0 Abundance/CI Lithophiles 0.5 Siderophiles Matrix Chalcophiles 0.0 500 1000 1500 2000 50% Condensation Temperature (K) (Wasson and Kallemeyn, 1988) Volatiles in matrix 350 CI 300 TL 250 CC CM 200 Non-CC 150 RC Bulk (ppm) Bulk Zn 100 CO,CV,CR OC 50 0 0 20 40 60 80 100 Matrix (vol.%) (Wasson and Kallemeyn, 1988; Rubin and Wasson 1993: Brown et al. 2000) Volatiles in matrix 4.5 4.0 TL CI 3.5 3.0 2.5 CM 2.0 1.5 CO,CV,CR Bulk Bulk C (wt.%) 1.0 OC 0.5 0.0 0 20 40 60 80 100 Matrix (vol.%) (Alexander et al. 2012,2014) Presolar grains in matrix (Xe-HL carried by supernova nanodiamonds) 2.5 CI 2.0 cc/g) 10 - 1.5 CM CV Xe HL (10 HL Xe 1.0 132 CO,CR 0.5 Bulk Bulk OC 0.0 0 20 40 60 80 100 Matrix (vol.%) (Huss and Lewis 1995; Huss et al. 2003) Volatiles in matrix 1.8 1.6 CI 1.4 1.2 CM 1.0 TL 0.8 0.6 CO, CR Bulk Bulk (wt.%)H 0.4 CV 0.2 OC 0.0 0 20 40 60 80 100 Matrix (vol.%) (Alexander et al. 2012) Story so far • The abundances of highly volatile elements, organic C, presolar circumstellar grains and water suggest that matrices in ALL chondrites are dominated by ~CI-like material. • If correct, since the ECs, OCs & RCs all formed ~2 Ma after CAIs: (1) CI-like material was present in the inner Solar System >2 Ma before a possible Grand Tack, and ~1 Ma after the inner Solar System was possibly sealed off by a growing Jupiter. (2) The snowline was already in the inner Solar System by 2 Ma. The main building blocks of the terrestrial planets may not have been initially volatile-free, but if formed <3-3.5 Ma after CAIs they were heavily modified by internal heating due to 26Al. D/H in H2O: an indicator of formation distance from the Sun? Interstellar H2O H2 Enceladus /(D/H) Comets H2O (D/H) Earth Turbulent mixing High T H2O Solar Horner et al. (2007) Distance from the Sun (AU) Rosetta results <10% to >90% of terrestrial 36Ar may be cometary (Marty et al. 2016) 22±5% of Xe from comets (Marty et al. 2017) Not primordial atmospheres 1100 900 Earth 700 500 300 N (‰) 15 d 100 Mars Earth Venus -100 -300 Solar -500 -1000 -500 0 500 1000 1500 dD (‰) d(‰)=(R/Rstd-1)x1000 R=D/H or 15N/14N Jaupart et al. (2017) – Ne, at least, in embryos not from primordial atmospheres.