A non-traditional stable isotope perspective

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1 The origins of the Moon: A non-traditional stable isotope perspective Fang-Zhen Teng Department of Earth and Space Sciences

2 From the beginning: The Universe: 13.8 Ga The Milky Way Galaxy The Solar System

3 The Present Solar System: Ga One star (The Sun) + nine planets + asteroids + Terrestrial planets Snow line Gaseous planets Moon

4 The Early Solar System When was the picture taken? Was the Earth differentiated? Was the Earth a closed system? Asteroid Early Moon Early Earth

5 The present Earth is highly differentiated

6 Major questions: Origin and evolution of the Earth The origin of the Earth The evolution of the atmosphere The mantle differentiation The making of the continental crust

7 Tools: Non-Traditional Stable isotopes Traditional isotopes: H, C, N, O, S Non-traditional: Li, Mg, Fe, Cu, Zn, Ti, Se, Tl

9 Tools: Non-Traditional Stable isotopes Traditional isotopes: H, C, N, O, S Non-traditional: Li, Mg, Fe, Cu, Zn, Ti, Se, Tl Traditional vs. Non-traditional isotopes Gas-source vs. MC-ICPMS (80 vs. 20 yrs) Non-Metal vs. metal Light vs. Heavy Large concentration variations in the Earth Fractionation mechanisms: covalent vs. ionic

10 Major questions: Origin and evolution of the Earth The origin of the Earth The evolution of the atmosphere The mantle differentiation The making of the continental crust

11 Outline The origin of the Earth Giant-impact Theory The evolution of the atmosphere Rise of atmospheric oxygen The mantle differentiation Magma transport rate The making of the continental crust Continental weathering

12 The Moon - Satellite of the Earth The Moon ¼ diameter of the Earth 1/100 mass of the Earth 3/5 density of the Earth

13 How did the Moon form? Giant impact! Hartmann and Davis 1975;Cameron and Ward 1976 Moon Mars-size proto Moon Earth Proto Earth

14 Detailed questions on giant-impact theory The nature of the impactor Where did the impactor come from? How big is the impactor? What is the composition of the impactor? Similar to Earth What happened during the impact When did it happen? Melting magma ocean? Evaporation gas? Or both? Well mixed between the impactor and proto-earth? Open or close system i.e., anything lost to space? After the impact: formation of the Moon and Earth Cool down condensation collision growth Moon? Are all elements/isotopes condensated at the same time? The source materials for the Moon: impactor or Earth s mantle?

15 Giant-impact theory A mars-size impactor >40% of the Moon-forming material from the impactor Impactor formed beyond the snow line

16 Snow line: where H-compounds (e.g., H 2 O) solid It separates terrestrial planets from gaseous planets Snow line

17 The impactor should have different composition! >40% of the Moon-forming material from the impactor The Moon inherited the impactor has different compositions Moon Moon vs. Earth Different bulk chemical composition Similar to Earth mantle Identical O isotopic composition Mittlefehldet et al 2008 Taylor and McLennan

18 The Moon/Earth have identical 17 O! The Moon and Earth have The slope identical is O 17 O isotopic composition but different from most of other planetary bodies Earth and Moon Mittlefehldet et al 2008

19 The Moon/Earth have identical Ti isotopic ratios! Zhang et al. 2012

20 Identical isotopic ratios for other elements! Cond. T. = at which elements condensate from solar nebula. Refractory elements = high cond. T Volatile elements = low cond. T.

21 Well-mixed between impactor and Earth Giant impact melt whole Earth mantle and impactor Form a magma disk and silicate vapor atmosphere Isotopes were well mixed before Moon formation Pahlevan and Stevenson 2007 EPSL

22 Do not work well for refractory elements Refractory elements are the last to evaporate during impact and the first to condensate during moon formation Moderately volatile elements (e.g., Cr, Mg and Fe) will be mixed within weeks. Refractory elements (e.g., Ti, W) will be mixed within 30 years The identical isotopic compositions of refractory elements require a long cooling time after the impact, which may not work

New Giant-impact models Halliday 2012 Small impactor theory: Cuk and Stewart 2012 Science Moon formed from Earth s mantle with 8% from impactor Large impactor theory:

23 New Giant-impact models Halliday 2012 Small impactor theory: Cuk and Stewart 2012 Science Moon formed from Earth s mantle with 8% from impactor Large impactor theory: Canup 2012 Science More vigorous impact mixed the impactor and Moon with about 1 to 1 mass ratio Resonance between the Sun and Moon invalidates the angular momentum requirements

24 If the new theory works, then isotopes of all elements should be well-mixed The Moon has a heavier Zn isotopic composition than Earth i.e., light Zn isotopes were lost during the Moon formation Zinc data are from Paniello et al 2012 Nature

25 The Moon is also depleted in volatile elements! Volatile elements are easier to lose during evaporation. Same is true for light isotopes Volatile elements were lost before Moon formation Moon 64 Zn 66 Zn K Taylor and McLennan 68 Zn U

26 K is also volatile and depleted in the Moon, but why its isotopes were not fractionated? We are developing a method to measure K isotopes with 10 times better precision, comparable to other elements Critical temperature at which isotope fractionation stops Error bar was too big to see (K data back to 1995)

27 Then isotopes of elements more volatile than Zn are expected to be fractionated Thallium We are developing a method to measure Tl isotopes at high precision for lunar samples

28 Summary on Moon formation Studies of non-traditional isotopes of both refractory and moderately volatile elements (Ti, Fe, Mg etc.) show identical compositions, suggesting the Moon formed from an Earth-like composition Zinc Isotope fractionation between the Earth and Moon suggests loss of volatile elements during giant impact Any giant-impact theories have to explain these isotopic signatures. Both recent models suggest a more significant proportion of Earth s mantle into the lunar formation More detailed isotopic studies and modeling are needed to better understand origin of the Moon

Reaching the Extremes of Planet Formation Shockwave Experiments in the Giant Impact Regime

Reaching the Extremes of Planet Formation Shockwave Experiments in the Giant Impact Regime Sarah T. Stewart Dept. Earth & Planetary Sciences, UC Davis Planet Formation Art by NASA Giant Impacts Art by