Origin of Earth s s Oceans. Karen Meech, Session #29 Tues 1/18/05

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1 Origin of Earth s s Oceans Karen Meech, Session #29 Tues 1/18/05

2 D/H Units Translation Absolute abundances harder to measure Measure relative to a standard S.M.O.W. for D/H = x 10-6 Definition δ = D/H sample D/H D/H SMOW Example: D/H SMOW LL3 meteorites: D/H = x 10-6 δd SMOW = -512 oo /o to oo /o X 1000 per mil

3 Most impt debate / controversy in SS form Oceans are enriched in Deuterium Comets brought some (10-30%) Isotopic Tracers D/H Earth ~ 16 x10-5 Solar System ~ 2.5x10-5 Comets ~ 30 x10-5 Origin of Earth s Water

4 Iceland Hawaii The D/H ratio in comets is not well established The reference to Earth is SMOW how does this relate to the primordial water?

$fractionation Comet formation$ scenarios Planetesimal delivery to

5 D/H Issues Original D/H set in big bang Formation of molecules in cold clouds Isotopic enrichment in cold interstellar clouds Ion-Molecule reactions Planetesimal formation fractionation Comet formation scenarios Planetesimal delivery to Earth Sources of Water D/H comet measurements Fractionation processes on Earth...? Deep Mantle Water? Measurements & Instrumentation

6 The Interstellar Medium Element Formation H, He form in big bang Heavier elements dust processed inside stars Cold clouds hot cores T ~ K n ~ 3 x 10 4 cm cm -3 Grains sites of molecule formation Collisions sticking Mobility of D and H is key

2 x 10-5 [δd = -910-858 oo /o] Protosolar Value D/H = 2.

7 D/H Measurements in Diffuse ISM Lyman α absorption toward several stars Local value D/H avg ~ 1.6 x 10-5 Range: x 10-5 [δd = oo /o] Protosolar Value D/H = 2.5 x 10-5 [δd = -839 oo /o] D/H at time of SS form 3 He/ 4 He in solar wind + D 3 He models Giant planets + models

Reactions Gas phase reactions D & H slight mass difference Closer E levels D favored in kinetics 1322 reactions

8 C 2 H 6 CH 3 CHO CH 3 COOH CO CO 2 CH 4 C 2 H 3 COCH 3 HCOOH H 2 O CH 3 OH H 2 S C 2 H 2 C 2 H 5 OH H 2 CO NH 3 C 2 H 4 Many molecules Chemical models Can t t decouple simple molecules ISM D/H Fractionation Ion Molecule Reactions Gas phase reactions D & H slight mass difference Closer E levels D favored in kinetics 1322 reactions / 107 species Energy levels not known for polyatomic molecules Reaction rates strongly T dependent time dependent

9 D Enrichment Primary Gas Phase Deuterium Reactions Certain reverse reactions in isotopic exchange are strongly inhibited at low T Results in preference for formation of certain deuterated species Rate coefficients, k cm 3 s -1 Reaction H HD H 2 D + + H 2 H 2 D + + H 2 H HD Gas-Grain Reactions 10K 1.7(-09) 3.6(-18) 30K 1.5(-09) 8.8(-12) 50K 1.5(-09) 9.3(-11) 70K 1.4(-09) 2.0(-10) Through accretion, D-molecules not destroyed as fast This leads to large deuterated molecule enhancement

ISM Core Measurements W33a D/H ~ (40-150) x 10-5 [δd=+1568+86308630 oo /o] Hot cores E barriers inhibiting reverse reactions overcome

10 ISM Core Measurements W33a D/H ~ (40-150) x 10-5 [δd= oo /o] Hot cores E barriers inhibiting reverse reactions overcome Accretion/surface chemistry Evaporation of grain mantles Preserved for ~ 10 4 yr Deuteration much stronger in low mass stars Orders of magnitude higher

Planetesimal formation Collapse of interstellar cloud

passes shock front sublimation, recondense Turbulent

gravitational clumping planet building Comets: how much

11 Planetesimal formation Collapse of interstellar cloud Center collapses faster flattened disk Grain infall passes shock front sublimation, recondense Turbulent mixing of gas / solids radial transport Eventual gravitational clumping planet building Comets: how much ISM material is preserved is the diff between SP and LP comets important for D/H?

12 Comets: Archaeological Remnants Kuiper Belt & Oort Cloud reservoir Perturbations close to sun Activity develops Km-scale nucleus Coma ~ 10 5 km Tail ~ km

13 ISM Alteration in Nebula? Re-equilibration of D/H Need heat k(t) ) drops 5 orders mag from T= K Need reservoir of Hydrogen gas No isotopic exchange between gas / solids Radial mixing of gas Reset D/H only in warm inner nebula How far out did turbulence extend?

14 Evidence for Radial Mixing Chemical heterogeneities H 2 CO in 1P/Halley Crystalline silicates Requires high T (> 800K) KBO dynamics planet migration

15 Comet Isotopic Measurements GHz High dry site: Mauna Kea Relate line strength to amt Excitation models Collisional excitation & LTE Fluorescence balance between excitation & vibrational-rotation decay Measure gas temperature Measure Q H2 O separately IR ro-vibrational bands UV (IUE) OH + models Ground narrow band OH Lyman α (SOHO) + models

D/H in Comets Comet Halley Halley Hyakutake Hale Bopp

Sub-mm Sub-mm Method Rosetta in situ Value x 10-5 30.

4 29 +/- 10 33 +/- 8 TBD TBD All measured so far are

16 D/H in Comets Comet Halley Halley Hyakutake Hale Bopp Tempel 1 Wirtanen Ion mass spec Neutral mass spec Sub-mm Sub-mm Sub-mm Method Rosetta in situ Value x / / / /- 8 TBD TBD All measured so far are from Oort cloud Prediction: KBO more enriched (less mixing in nebula) Sub-mm measurements very indirect

17 D/H Preserved During Sublimation? Sublimation of HDO and H 2 O from separate fronts Nucleus is porous Vapor pressures are equal (lab meas) ρ HDO < ρ H2 O HDO front moves inward faster HDO flux decreases faster Steady state eventually reached D/H meas = D/H nucleus Far from steady state D/H can be a factor of 2 high Steady state near q, different if far from q

Meteorite D/H Measurements Meteorites Water-rich

(7-45) x 10-5 [δd = -550+1 +1889 oo Earth /o]

18 Meteorite D/H Measurements Meteorites Water-rich minerals in some Form within 1-2 Myr of SS form Evidence for heating & aqueous alteration D/H Measurements Chondrules in LL3 D-rich meteorites: (7-45) x 10-5 [δd = oo Earth /o] Chondrites (12-30) x 10-5 [δd = oo /o] D/H x 10-5

$preferential H atm escape Jeans Escape High E tail of Maxwell v distn escapes Mars D/H fractionation Loss$ of 2.7x10 8 cm -2 s -1 on Earth, small compared to reservoir Loss on Mars of 2.

of 2.7x10 8 cm -2 s -1 on Earth, small compared to reservoir Loss on Mars of 2.

19 Mars SNC Meteorites Atmospheric water: D/H = 81 x 10-5 (δd=+4200 oo /o) May be enriched because of preferential H atm escape Jeans Escape High E tail of Maxwell v distn escapes Mars D/H fractionation Loss of 2.7x10 8 cm -2 s -1 on Earth, small compared to reservoir Loss on Mars of 2.4x10 8 cm -2 s -1 Reservoir unknown Log of water in Mars crust today (H 1 ) versus early Mars, (H o ) for D/H ratios wrt SMOW of 2.6 & 5.2

20 Dynamical Delivery of Meteoritic Material Dynamical models (Morbidelli( Morbidelli) delivery in few impacts (small number statistics) Secular resonances & planet migration + gas drag: delivers H 2 O-rich asteroids to Earth Models show only 2-20% of cometary bodies were delivered to Earth Problem with Nobel gas abundances Earth has too much Ne to come from asteroids, but maybe not comets

21 Summary of D/H Measurements SMOW Comets Source Diffuse ISM Protosolar Nebula Meteorites Molecular clouds / hot cores [δd oo oo /o] > D/H x x x x x 10-5 > x 10-5

22 Status of D/H Measurements?? We don t t really know comet D/H for more than one type Meteorite measurements have wide range Dynamics of delivery? Nobel gas abundances? Does SMOW represent the primordial water on Earth?

$What are fractionation processes on Earth for D/H?$

23 Earth s s Juvenile Water? Are there sources of Deep Mantle primordial water? What are fractionation processes on Earth for D/H? Lack of re-equilibration: no source of H How to assess contamination in mantle water measurements? If water is delivered during impact is the D/H reset?

24 How to Access Primordial Water? Glacier & Geothermal systems Gas phase measurements? Take Advantage of drilling High T rock phases surviving transport Olivine, pyroxene, diamond 3 He/ 4 He in phenocrysts Xenoliths: δd = -40 to -95 oo oo /o

25 Fractionation Processes on Earth Evaporation / condense Light molecules enriched in vapor phase Kinetic effects Rate of chemical reaction related to mass Diffusion Light isotopes more mobile Pressure Hydrous minerals D/H fractionation Chemical composition Nature of chemical bonds high vibration f prefer heavier isotopes Crystal structure Heavy isotopes concentrate in more closely packed structures MORB water Homogeneous wrt % water Remixed into source or uniform degassing Hot spots and xenoliths significant hydration in mantle Upper mantle *may* contain primordial H 2 O Hydrosphere UV photochemistry Impact degassing subduction

26 Deep Drilling Projects HSDP Hilo 4 km (ongoing) Isotopic data vs time: plume geochemistry IDDP Iceland 5 km (start 11/04) Extraction of Energy & chemicals o C Instruments Small down-hole mass spec Boreholes 4 4 diam

27 Hawaii Scientific Drilling Project Continuous samples from MKO flows Learn how mantle plumes originate & magma to surface Drill from ,000 yr (20,000 ft) Zoned plume Core from deep mantle

28 Iceland Deep Drilling Project Plan (economic) Depth of geothermal resources 5 km well in Rekjanes peninsula (2007-8) 3 wells, 15 yr Krepla Problems for primordial water search Rocks are very permeable Fluid origins seawater? Water-rock exchange? Permeability at depth unknown Suggested tactics Gas inclusions in phenocrists Sampling new volcanic plumes Gas samples disappear quickly

29 Grimsvotn Eruption Nov 2004

30 Does a Habitable World Require an Asteroid Belt? Implications for terrestrial planet H 2 O in other SS require an asteroid belt? Oort cloud?

31 Discussion Nordic Ctr for Volcanology: Karl Gronvold, Niels Oskarsson Look for D/H in high T phases H released from deep sources from breakdown of hydrides Interaction with C CH 4 At high T (1500K) no fractionation Gases trapped in inclusion in spinels, olivines,, diamonds Measurements H with ion beams (SIMS) H measurement tricky (need clean system) D very challenging 3 He/ 4 He anomalies in Iceland and Hawaii Questions Timescale for planetary chemical fractionation & core formation?

32 Discussion Nordic Ctr for Volcanology: Karl Gronvold, Niels Oskarsson Surtsey gas analysis Rare gas work Probably recycled seawater Helium work Primordial He high in NW & central Iceland Geothermal water Isotopic work Iceland Mostly meteoric Except Reykjanes peninsula (δd=-20%)( Rocks very permeable

Comet Science Goals II

Comet Science Goals II {questions for goals} Don Brownlee Did the events postulated by the Nice Hypothesis really happen? Were there wide-spread solar system wide impact events that were coeval with the