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Water Delivery & D/H ratios in the Solar System How did Earth get its Water?

Water Delivery & D/H ratios in the Solar System How did Earth get its Water?. Ricky Nilsson Department of Astronomy Stockholm University SwAN meeting, May 18, 2009. Outline Introduction: The importance of water in Astrobiology Planet formation and water delivery:

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Water Delivery & D/H ratios in the Solar System How did Earth get its Water?

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  1. Water Delivery & D/H ratios in the Solar SystemHow did Earth get its Water? Ricky Nilsson Department of Astronomy Stockholm University SwAN meeting, May 18, 2009

  2. Outline • Introduction: The importance of water in Astrobiology • Planet formation and water delivery: How did Earth get its water? Evidence and prime suspects • Uncertainties in measurements of D/H ratios • Future activities: What have been done and what can we add? Water Delivery & D/H ratios in the Solar System SwAN meeting, May 18, 2009

  3. Introduction Planet formation & Water delivery D/H measurements Future The importance of water in Astrobiology Requirements for Life: carbon compounds, free energy, liquid water Water has unique properties: bipolarity  hydrogen bonds, excellent solvent, liquid over broad range of temperatures, high heat capacity, high surface tension, maximum density above liquid-solid phase transition temperature. Look for liquid H2O to find habitable environments Water is a key player in interstellar chemistry, geochemistry (and dynamics), and biochemistry Credit: UNSW 2007 Water Delivery & D/H ratios in the Solar System SwAN meeting, May 18, 2009

  4. Introduction Planet formation & Water delivery D/H measurements Future • Water and interstellar chemistry • H2O forms in cold GMCs • Layer of ice (mainly of H2O, but also • CH4, NH3, CO and CO2) covers the • grains • Chemical reactions on and in ice • under influence of ionizing radiation • Large and complex molecules Almost 150 species observed (Size: 2-13 atoms) Mottl et al. (2007) Fraser et al. (2002) Water Delivery & D/H ratios in the Solar System SwAN meeting, May 18, 2009

  5. Introduction Planet formation & Water delivery D/H measurements Future • Water and geodynamics • The structure of Earth • Early differentiation • layered interior structure of Earth • Temperature and pressure • determine melting point and • viscosity • Water an important factor influ- • encing viscosity and dynamics • of outer core and mantle material http://earth.unh.edu/esci402/docs/Earth%20Interior.jpg Water Delivery & D/H ratios in the Solar System SwAN meeting, May 18, 2009

  6. Introduction Planet formation & Water delivery D/H measurements Future Water and geodynamics Inventories of water Core: 1∙1022 - 1.4∙1023 kg Mantle/crust: 3.6∙1021 – 8.3∙1021 kg Hydrosphere/atmosphere: 1.4∙1021 kg The dynamo mechanism in Earth’s liquid iron core generates protective global magnetic field. Magnetic field shields surface life from harmful radiation (and protects volatiles in atmosphere), shapes cycles related to atmospheric stability, surface conditions and interior dynamics. Self-exciting dynamo Glatzmaier & Roberts (1995) Water Delivery & D/H ratios in the Solar System SwAN meeting, May 18, 2009

  7. Introduction Planet formation & Water delivery D/H measurements Future • Water and geodynamics • The hydrosphere • Water on surface and in • atmosphere (97% in oc- • eans) • Atmospheric H2O • dominant greenhouse gas • The hydrological cycle • Connected to biosphere • and deeper geodynamic Water Delivery & D/H ratios in the Solar System SwAN meeting, May 18, 2009

  8. Introduction Planet formation & Water delivery D/H measurements Future Water and geodynamics Plate tectonics Lithosphere broken up into several plates moving on convecting asthenosphere. Different boundaries: conservative (earthquakes), constructive (sea-floor spr- eading), destructive (volcanism, mountain ranges) Driven by gravity and friction http://www.scarborough.k12.me.us/wis/teachers/dtewhey/webquest/nature/images/convectioncurrent.gif Water Delivery & D/H ratios in the Solar System SwAN meeting, May 18, 2009

  9. Introduction Planet formation & Water delivery D/H measurements Future • Water and geodynamics • What role does water play? • Initiates subduction • Acts as “lubricant” for slab slide • Lowers viscosity of mantle • Plate tectonics rely on the presence of • water! Regenauer-Lieb (2001) Geodynamical regimes Van Thienen et al. (2007) http://records.viu.ca/~earles/breakoff.gif Water Delivery & D/H ratios in the Solar System SwAN meeting, May 18, 2009

  10. Introduction Planet formation & Water delivery D/H measurements Future Water and life What is life? No broadly accepted definition exists, but the basic requirements are known: liquid water, CHON building blocks, energy. The living cell Water transports nutrients and waste (solves polar molecules and salts), regulates temperature, concentrates sol- utions of solids on the cell wall. Water permits hydrophobic organic mole- cules to form cellular membranes. http://www.williamsclass.com/SeventhScienceWork/ImagesCells/EukaryoticCell.jpg Water Delivery & D/H ratios in the Solar System SwAN meeting, May 18, 2009

  11. Introduction Planet formation & Water delivery D/H measurements Future Water and life The biosphere All living organism, their connections, and their interactions with the lithosphere, hydrosphere, atmosphere. Water plays a crucial role! Gaia hypothesis Is the biosphere a living organism? Lovelock noted the complex interaction of biotic and abiotic factors in the biosphere, acting to regulate climatic and biogeochemical conditions on Earth (Lovelock & Margulis 1974). E.g. constant salinity of ocean water regulated by organic processes, and carbon cycle (requires water and life). Water Delivery & D/H ratios in the Solar System SwAN meeting, May 18, 2009

  12. Introduction Planet formation & Water delivery D/H measurements Future Water and life Early life and conditions on early Earth: First evidence of water Investigation of zircon crystals formed 4.2-4.4 Ga ago (during the Hadean) have revealed that large amounts of liquid water must have been present by then (Harrison & Watson 2005). However, this time was characterized by large impacts. Hydrosphere was destroyed? Liquid water was present, so life could have originated (multiple times?). Where did the water come from? Valley et al. (2002) Water Delivery & D/H ratios in the Solar System SwAN meeting, May 18, 2009

  13. Introduction Planet formation & Water delivery D/H measurements Future Water in the protoplanetary disk The snow line Water ice sublimates at T ~ 145-180 K  snow line at ~ 2 AU (Lecar et al. 2006). Outside the snow line Colder temperatures, ices (including H2O) give more material for planet formation, fast growth and gas accretion  giant planets Inside the snow line Higher temperatures, no ices means less solids for planet formation, slower growth, dust  pebbles  rocks  planetesimals  terrestrial planets Where did current H2O come from? http://www.astro.virginia.edu/class/oconnell/astr121/im/solarneb-frostline-TSmith.jpg Water Delivery & D/H ratios in the Solar System SwAN meeting, May 18, 2009

  14. Introduction Planet formation & Water delivery D/H measurements Future Competing theories • Wet accretion – water from nebula incorporated into rocks (e.g. Drake, 2005)‏ • Ingassing from nebula into hot proto-Earth (e.g. Sasaki 1999, Ikoma & Genda 2006)‏ • Icy protoplanets colliding with the proto-Earth (Morbidelli et al. 2000)‏ • Icy planetesimals (comets or asteroids) falling onto already existing planet (late veneer) (Delsemme 1999, 2000)‏ Water Delivery & D/H ratios in the Solar System SwAN meeting, May 18, 2009

  15. Introduction Planet formation & Water delivery D/H measurements Future Comets and asteroids in the Solar System Asteroid Belt: 2.2-3.4 AU from Sun, could not accrete due to Jupiter, 1-2∙106 objects >1 km Kuiper Belt: short-period comets, 30-55 AU from Sun, some formed at present location, some scattered, 1011 objects >100 km 105 objects >1 km Oort Cloud: long-period comets, 20,000-50,000 AU from Sun, scattered to present location, trillions of objects >1.3 km but far apart Credit: NASA/JPL-Caltech/R.Hurt Water Delivery & D/H ratios in the Solar System SwAN meeting, May 18, 2009

  16. Introduction Planet formation & Water delivery D/H measurements Future Water in asteroids and comets Asteroids Remote sensing of asteroids and laboratory studies of chondrites imply: - Most main belt asteroids consist of anhydrous silicates, metal, and sulfides - Most asteroids located at >3 AU consist of hydrated silicates, organic matter, carbonates, sulfates, and iron oxides Comets Remote and in situ studies reveal: 20-80% water in comets. However, only three objects (all from the Oort Cloud) have been investigated. How do we determine the contribution from these sources? D/H ratio used as principal discriminator (but also abundances and isotope ratios of noble gases and siderophile elements) Water Delivery & D/H ratios in the Solar System SwAN meeting, May 18, 2009

  17. Introduction Planet formation & Water delivery D/H measurements Future The D/H ratio Big Bang set initial D/H value. Local enhancements due to chemical fractionation processes. Measurements of three (Oort Cloud) comets show 2x the SMOW value, but carbonaceous chondrites match. Low- temperature ion-molecule reactions Mottl et al. (2007) Water Delivery & D/H ratios in the Solar System SwAN meeting, May 18, 2009

  18. Introduction Planet formation & Water delivery D/H measurements Future Measurements of the D/H ratio to find sources of Earth’s water Drake & Campins (2006) Water Delivery & D/H ratios in the Solar System SwAN meeting, May 18, 2009

  19. Introduction Planet formation & Water delivery D/H measurements Future Uncertainties in measurements of the D/H ratio How certain are these values for Earth ocean water? How certain are these values for comet and asteroid water? D/H fractionation on Earth D/H ratios might depend on: • Ice • Geological and geochemical processes (outgassing) • Life (bacteria, plants, etc.) • Atmospheric loss • Measured D/H ratio in ocean might not reflect the global value • Where should we look to find D/H ratios representative of early Earth? • Deep magma sources • Ancient rocks Water Delivery & D/H ratios in the Solar System SwAN meeting, May 18, 2009

  20. Introduction Planet formation & Water delivery D/H measurements Future D/H fractionation in the Solar System Main-Belt comets A third reservoir of comets in the outer main-belt (Hsieh & Jewitt 2006). Could they have a lower D/H ratio, matching the SMOW value? Dynamically more plausible than Kuiper Belt and Oort Cloud comets. Herschel Space Telescope: D/H ratio of outer planets and comets Credit : ESA/ AOES Medialab Water Delivery & D/H ratios in the Solar System SwAN meeting, May 18, 2009

  21. Introduction Planet formation & Water delivery D/H measurements Future Future activities • Literature review: what measurements have been done? • Workshop planned for November 3 2009, in connection with SwAN meeting in Stockholm Co-investigators: Andrej Kuutmann (Astronomy, SU) Paula Lindgren (Geology, SU) Wolf D. Geppert (Physics, SU) Marc Hoeppner (Biology, SU) Henrik Johansson (Physics, SU) Hans Olofsson (Astronomy, Onsala) Welcome to contribute! Water Delivery & D/H ratios in the Solar System SwAN meeting, May 18, 2009

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