Volatiles in the terrestrial planets Sujoy Mukhopadhyay University of California, Davis CIDER, 2014 Atmophiles: Elements I will talk about rock-loving iron-loving sulfur-loving Temperatures in Protoplanetary Disk 1 AU ~= 149,597,870 km K/Th ratio of the terrestrial planets Peplowski et al., Science, (2011) K/Th ratio of the terrestrial planets Peplowski et al., Science, (2011) What about the H, C, N, noble gases? Questions regarding volatiles on the terrestrial planets that we can answer • What are the potential volatile sources? • What processes could have sculpted the volatile budget? • When could volatiles be delivered? Questions regarding volatiles on the terrestrial planets that we would really like to answer What are the volatile compositions and budgets? What are the volatile sources? What are the processes that sculpted the volatile budget? When were the volatiles delivered? What are the potential volatile sources? 1) Acquiring nebular (solar) volatiles • Capture of nebular gases after nebula disperses, heavier components of nebular atmosphere retained; rocky mantles equilibrate with nebular atmospheres through a magma ocean. • Irradiation of grains with solar radiation. Lifetime of nebular gas Mamajek, 2009 Mars accretion timescale Dauphas and Pourmand, 2011 What are the potential volatile sources? 2) Acquiring chondritic volatiles Planetesimal accretion adds an isotopic signature (e.g., in N, water and noble gases) that is distinct from the solar nebula. What are the potential volatile sources? 3) Acquisition of volatiles from icy planetesimals Icy planetesimals may add volatiles with distinct H and N isotopic composition compared to chondritic and solar volatiles Feeding zone of terrestrial planets Raymond et al., 2009 Processes that lead to volatile loss during accretion • Hydrodynamic escape (produces a mass fractionated residual atmosphere) Processes that lead to volatile loss during accretion • Hydrodynamic escape (produces a mass fractionated residual atmosphere) Energy input (EUV flux) into upper atmosphere drives thermal loss of light constituent (H2) Escaping flux of H2 can be high enough to exert upward drag on heavier species and lift them out of atm. Mass dependent process: so fractionating atm loss process i 84 i 84 y‐axis = (( Kr/ Kr)sample/( Kr/ Kr)air‐1) X 1000 Pepin & Porcelli 2002 Processes that lead to volatile loss during accretion • Hydrodynamic escape (produces a mass fractionated residual atmosphere) • Impacts – Giant impacts (isotopes are not mass fractionated; elements maybe fractionated depending upon their distribution between atmosphere‐ocean) – Planetesimal impacts (isotopes are not mass fractionated; elements maybe fractionated; Schlichting et al., Icarus, in press) Loss Is Important in Planetary Formation Significant atm loss without an ocean only in most energetic impacts Atmospheric loss with an ocean likely over the energy range of planet formation Loss limited in canonical moon forming impact Significant loss possible in high angular momentum impacts Velocities from Raymond et al. 2009 Reservoirs can be Fractionated in Impacts Atmosphere lost preferentially compared to an ocean H retained in ocean; Noble gases and N (C?) lost in atmosphere When could volatiles have been delivered? The two end‐member cases: 1. During the main phase of accretion; i.e., pre‐Moon forming giant impact – Giant impacts can lead to bulk accretion or erosion of volatiles. Re‐equilibration of magma ocean with the new atmosphere. When could volatiles have been delivered? The two end‐member cases: 1. During the main phase of accretion; i.e., pre‐Moon forming giant impact – Giant impacts can lead to bulk accretion or erosion of volatiles. Re‐equilibration of magma ocean with the new atmosphere. 2. Associated with a late veneer All sorts of combinations within the end‐member cases are possible How do we go about establishing volatile inventories? Venus composition Mass spectrometers on Venera 13 and 14 missions and the NASA Pioneer mission Mars composition • Surface compositions and inventories: Viking, Odessey, MSL • Surface and interior compositions: Martian meteorites Earth composition Interior inventory from basalts A vesicular subaerial basalt A gas rich popping glass recovered from the bottom of the ocean Correct C/N ratio using rare gas fractionation N2/40Ar does not change as a function of degassing Increasing degassing Marty, 1995 10±5 oceans 1.7±0.3 oceans Halliday, 2013 Halliday, 2013 Comparison of volatile abundance patterns 1e+0 1e-1 Earth Venus 1e-2 Mars Sun 1e-3 CI Si) 1e-4 6 1e-5 1e-6 1e-7 Y Data 1e-8 Si)/(M/10 1e-9 6 1e-10 1e-11 (M/10 1e-12 1e-13 1e-14 2020NeNe 36 36ArAr 84 84KrKr 14 14NN 12 12CC After Halliday, 2013 Halliday, 2013 Comparison of volatile abundance patterns 1e+0 1e-1 Earth Venus 1e-2 Mars Sun 1e-3 CI Si) 1e-4 6 1e-5 1e-6 1e-7 Y Data 1e-8 Si)/(M/10 6 1e-9 1e-10 1e-11 (M/10 1e-12 1e-13 1e-14 2020NeNe 36 36ArAr 84 84KrKr 14 14NN 12 12CC Evidence for accretion of solar volatiles in deep mantle Iceland: Mukhopadhyay, 2012; DM Holland and Ballentine, 2006; (Adapted from Marty, 2012; Mukhopadhyay et al., in prep). Evidence for hydrodynamic escape? Iceland: Mukhopadhyay, 2012; DM Holland and Ballentine, 2006; (Adapted from Marty, 2012; Mukhopadhyay et al., in prep). H and N composition of Earth Earth volatiles: Signature of Solar, comets or chondritic meteorites? Marty, 2012 Earth’s hydrogen budget: mainly acquired during main phase of accretion and sculpted by impacts. Isotopic ratios of H, C, N, Cl are chondritic Elemental H/N ratio is not Water may have been mostly accreted prior to the last giant impact; ~80% (also see Halliday, 2013). Impacts (large and small) and the different outcomes of impact events shaped early terrestrial atmospheres..