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The Tethered MoonA reasonable initial condition on Earth after the Moonforming impact is that it begins as a hot global magma ocean1,2. We therefore begin our study with the mantle as a liquid ocean with a surface temperature on the order of 3000- 4000 K at a time some 100-1000 years after the impact, by which point we can hope that early transients have settled down. A 2nd initial condition is a substantial atmosphere, 100-1000 bars of H2O and CO2, supplemented by smaller amounts of CO, H2, N2, various sulfur-containing gases, and a suite of geochemical volatiles evaporated from the magma. Third, we start the Moon with its current mass at the relevant Roche limit. The 4th initial condition is the angular momentum of the Earth-Moon system. Canonical models hold this constant, whilst some recent models begin with considerably more angular momentum than is present today. Here we present a ruthlessly simplified model of Earth's cooling magmasphere based on a full-featured atmosphere and including tidal heating by the newborn Moon. Thermal blanketing by H2O-CO2 atmospheres slows cooling of a magma ocean. Geochemical volatiles - chiefly S, Na, and Cl - raise the opacity of the magma ocean's atmosphere and slow cooling still more. We assume a uniform mantle with a single internal (potential) temperature and a global viscosity. The important "freezing point" is the sharp rheological transition between a fluid carrying suspended crystals and a solid matrix through which fluids percolate. Most tidal heating takes place at this "freezing point" in a gel that is both pliable and viscous. Parameterized convection links the cooling rate to the temperature and heat generation inside the Earth. Tidal heating is a major effect. Tidal dissipation in the magma ocean is described by viscosity. The Moon is entwined with Earth by the negative feedback between thermal blanketing and tidal heating that comes from the temperature-dependent viscosity of the magma ocean. Because of this feedback, the rate that the Moon's orbit evolves is limited by the modest radiative cooling rate of Earth's atmosphere, which in effect tethers the Moon to the Earth. Consequently the Moon's orbit evolves orders of magnitude more slowly than in conventional models. Slow orbital evolution promotes capture by orbital resonances that may have been important in the Earth-Moon system
Document ID
20140010765
Acquisition Source
Ames Research Center
Document Type
Conference Paper
Authors
Zahnle, Kevin (NASA Ames Research Center Moffett Field, CA United States)
Lupu, Roxana Elena (Bay Area Environmental Research Inst. Moffett Field, CA, United States)
Dubrovolskis, A. R. (Bay Area Environmental Research Inst. Moffett Field, CA, United States)
Date Acquired
August 18, 2014
Publication Date
June 8, 2014
Subject Category
Astronomy
Report/Patent Number
ARC-E-DAA-TN14502
Meeting Information
Meeting: NCTS#18576-14 Goldschmidt Conference
Location: Sacramento, CA
Country: United States
Start Date: June 8, 2014
End Date: June 13, 2014
Sponsors: European Association of Geochemistry, Geochemical Society
Funding Number(s)
CONTRACT_GRANT: NNX14AB66A
WBS: WBS 811073.02.04.03.75
CONTRACT_GRANT: NNX13AD56A
Distribution Limits
Public
Copyright
Public Use Permitted.
Keywords
Earth-Moon system
H2O-CO2 atmospheres
magma ocean

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