Evaporation from the Lunar Magma Ocean Was Not the Mechanism for Fractionation of the Moon’s Moderately Volatile Elements

Tang, Haolan; Young, E. D.

doi:10.3847/psj/abb23c

Cited by 16 publications

(40 citation statements)

References 81 publications

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“…The light composition of the former require temperatures > 1600 K (to vaporise sufficient Cr) but < 1800 K to produce sufficient isotope fractionation where near-equilibrium conditions had to have prevailed during vaporisation. In addition, the Li/Na and Cr constraints yield similar temperatures to those obtained by thermal models of the near-surface melt (Tang and Young 2020).…”

Section: Influence Of Evaporation On the Na K And Zn Abundances In The Moonsupporting

confidence: 63%

“…The range of fluxes and tidal expansion timescales computed above permits evaluation of how the residual composition of the Moon evolves as a result of atmospheric escape. Given that the initial bulk composition of the Moon is likely similar to that of the bulk silicate Earth (BSE) (Ringwood et al 1987), and presuming that the composition of the escaping vapour is that of the vapour at the liquid-gas interface (neglecting molecular diffusion in the outgoing flux, that is negligible in a hydrodynamic wind, see Tang and Young (2020)), the effect of atmospheric loss on the composition of the Moon may be estimated.…”

Section: Vapour Pressures Of Metal-bearing Gases Above the Silicate Moonmentioning

confidence: 99%

“…When the stagnant lid forms we assumes that the outgoing flux drops to 0. Previous studies suggest that the lid may form in ∼ 1000 years only (Elkins-Tanton et al 2011;Tang and Young 2020) where σ SB is the Stefan-Boltzmann constant. T ⊕ is black-body temperature of the Earth.…”

Section: Figuresmentioning

confidence: 99%

“…In Tang and Young (2020) (TY20 hereafter) it is argued that the pressure of the evaporating material above the lunar magma ocean is about 10 −7 bar, far below its saturated vapour pressure (∼ 10 −3 bar at ∼ 2000K). This conclusion is reached by finding the pressure at which the escaping flux at the top of the atmosphere (namely, the point of escape; the Bondi radius) yields an escape rate that can be sustained by diffusive transport of the evaporated material through the atmosphere.…”

Section: What Is the Net Evaporative Flux And Pressure Above The Magma Ocean ?mentioning

confidence: 99%

“…Indeed Equation 6of Richter et al (2002) is simply Fick's law of mass diffusion, applied to a dilute species (the evaporating gas) diffusing through an ambient medium (a gas, in this case) with a fixed diffusion coefficient that remains constant with distance from the surface. The analytical solution to this equation is reported in Equation 6of Young et al (2019) and Equation 4of Tang and Young (2020). Richter et al (2002) shows that at steady-state (t → +∞), the far-field pressure (as defined above) is lower than the vapour pressure (P sat (T )) of the evaporating species at the evaporative surface.…”

Section: What Is the Net Evaporative Flux And Pressure Above The Magma Ocean ?mentioning

confidence: 99%

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Tidal pull of the Earth strips the proto-Moon of its volatiles

Charnoz¹,

Sossi²,

Lee³

et al. 2021

Icarus

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Prevailing models for the formation of the Moon invoke a giant impact between a planetary embryo and the proto-Earth (Canup 2004;Ćuk et al. 2016). Despite similarities in the isotopic and chemical abundances of refractory elements compared to Earth's mantle, the Moon is depleted in volatiles (Wolf and Anders 1980). Current models favour devolatilisation via incomplete condensation of the proto-Moon in an Earth-Moon debris-disk (Charnoz and Michaut 2015;Canup et al. 2015;Lock et al. 2018). However the physics of this protolunar disk is poorly understood and thermal escape of gas is inhibited by the Earth's strong gravitational field (Nakajima and Stevenson 2014). Here we investigate a simple process, wherein the Earth's tidal pull promotes intense hydrodynamic escape from the liquid surface of a molten proto-Moon assembling at 3-6 Earth radii. Such tidally-driven atmospheric escape persisting for less than 1 Kyr at temperatures ∼ 1600 − 1700 K reproduces the measured lunar depletion in K and Na, assuming the escape starts just above the liquid surface. These results are also in accord with timescales for the rapid solidification of a plagioclase lid at the surface of a lunar magma ocean (Elkins-Tanton et al. 2011). We find that hydrodynamic escape, both in an adiabatic or isothermal regime, with or without condensation, induces advective transport of gas away from the lunar surface, causing a decrease in the partial pressures of gas species (P s ) with respect to their equilibrium values (P sat ). The observed enrichment in heavy stable isotopes of Zn and K (Paniello et al. 2012; Wang and Jacobsen 2016) constrain P s /P sat >0.99, favouring a scenario in which volatile loss occurred at low hydrodynamic wind velocities (< 1% of the sound velocity) and thus low temperatures. We conclude that tidally-driven atmospheric escape is an unavoidable consequence of the Moon's assembly under the gravitational influence of the Earth, and provides new pathways toward understanding lunar formation.

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Section: Influence Of Evaporation On the Na K And Zn Abundances In The Moonsupporting

confidence: 63%

Section: Vapour Pressures Of Metal-bearing Gases Above the Silicate Moonmentioning

confidence: 99%

Section: Figuresmentioning

confidence: 99%

Section: What Is the Net Evaporative Flux And Pressure Above The Magma Ocean ?mentioning

confidence: 99%

Section: What Is the Net Evaporative Flux And Pressure Above The Magma Ocean ?mentioning

confidence: 99%

See 3 more Smart Citations