DOI: 10.1016/j.epsl.2017.10.026
Scopus记录号: 2-s2.0-85033576027
论文题名: Iron snow in the Martian core?
作者: Davies C.J. ; Pommier A.
刊名: Earth and Planetary Science Letters
ISSN: 0012821X
出版年: 2018
卷: 481 起始页码: 189
结束页码: 200
语种: 英语
英文关键词: dynamo action
; iron snow
; Mars’ core
Scopus关键词: Entropy
; Interactive devices
; Iron
; Liquids
; Magnetism
; Crystallization regimes
; Dynamo action
; General theory
; Geodetic constraints
; Gravitational energy
; Liquidus temperature
; Magnetic history
; Sulfur concentrations
; Snow
; geodynamo
; iron
; magnetic field
; Mars
; planetary atmosphere
; stratification
; thermochemistry
英文摘要: The decline of Mars’ global magnetic field some 3.8–4.1 billion years ago is thought to reflect the demise of the dynamo that operated in its liquid core. The dynamo was probably powered by planetary cooling and so its termination is intimately tied to the thermochemical evolution and present-day physical state of the Martian core. Bottom-up growth of a solid inner core, the crystallization regime for Earth's core, has been found to produce a long-lived dynamo leading to the suggestion that the Martian core remains entirely liquid to this day. Motivated by the experimentally-determined increase in the Fe–S liquidus temperature with decreasing pressure at Martian core conditions, we investigate whether Mars’ core could crystallize from the top down. We focus on the “iron snow” regime, where newly-formed solid consists of pure Fe and is therefore heavier than the liquid. We derive global energy and entropy equations that describe the long-timescale thermal and magnetic history of the core from a general theory for two-phase, two-component liquid mixtures, assuming that the snow zone is in phase equilibrium and that all solid falls out of the layer and remelts at each timestep. Formation of snow zones occurs for a wide range of interior and thermal properties and depends critically on the initial sulfur concentration, ξ0. Release of gravitational energy and latent heat during growth of the snow zone do not generate sufficient entropy to restart the dynamo unless the snow zone occupies at least 400 km of the core. Snow zones can be 1.5–2 Gyrs old, though thermal stratification of the uppermost core, not included in our model, likely delays onset. Models that match the available magnetic and geodetic constraints have ξ0≈10% and snow zones that occupy approximately the top 100 km of the present-day Martian core. © 2017 The Authors Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/110176
Appears in Collections: 影响、适应和脆弱性 气候变化事实与影响
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作者单位: School of Earth & Environment, University of Leeds, Leeds, LS2 9JT, United Kingdom; Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, University of California at San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0225, United States
Recommended Citation:
Davies C.J.,Pommier A.. Iron snow in the Martian core?[J]. Earth and Planetary Science Letters,2018-01-01,481