A New Paradigm for Planetary Evolution? Lunar Structure and Composition Explained by the South Pole–Aitken Impact

Jones, Matt John

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Year:: 2024
Contributor:: Jones, Matt John (creator); Evans, Alexander (Advisor); Liang, Yan (Reader); Daubar, Ingrid (Reader); Bergen, Karianne (Reader); Johnson, Brandon (Reader); Brown University. Department of Earth, Environmental, and Planetary Sciences (sponsor)
Genre:: theses
Subject:: Geodynamics; Heat--Convection--Mathematical models; Moon; Planetary science; Planets--Crust; Planets--Mantles
Extent:: xii, 135 p.

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Abstract:: Earth’s Moon, when viewed from Earth, always shows the same face. The compositional, topographic, and structural asymmetry between the Moon’s nearside and farside hemispheres has remained a multifaceted and fundamental mystery of lunar science since the first viewing of the lunar farside in the mid-20th century. We investigate the role of the ancient lunar South Pole–Aitken (SPA) basin-forming asteroid impact—a highly energetic event with myriad consequences—in driving the dynamical and compositional evolution of the Moon to bring about the lunar asymmetry observed today. Using a 3-D, spherical, finite element code to simulate hundreds of millions of years of the lunar mantle’s early dynamical evolution, we demonstrate that widespread shock-induced heating from the SPA impact event can catalyze lunar mantle convection patterns that concentrate particular materials of interest (distinct rock compositions with enhanced abundances of heat-producing elements and other geochemically “incompatible” elements) beneath the nearside hemisphere and can trigger large convective upwellings of other materials of interest (magnesium-enriched rock compositions that initially formed deep in the lunar mantle)—each process being a prerequisite for various modern observations. Furthermore, we use simple mathematical models of isostasy and thermally driven pore space closure in the Moon’s crust to demonstrate that SPA’s dynamical consequences can reduce or eliminate the need for a commonly invoked nearside-farside asymmetry in crustal thickness, which itself is a facet of the lunar asymmetry that has long remained without a widely agreed-upon explanation. Altogether, our analyses and conclusions are self-consistent and, for the first time, name a known event in lunar history as a singular catalyst for the origin of an array of lunar observations previously attributed to disparate processes. While the lunar asymmetry cannot be entirely attributed to SPA before further investigation, our work suggests the possibility of a paradigm shift toward understanding rocky planet evolution as driven by the consequences of highly energetic asteroid impacts expected to occur during the early history of most planets.
Notes:: Thesis (Ph. D.)--Brown University, 2024

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Citation

Jones, Matt John, "A New Paradigm for Planetary Evolution? Lunar Structure and Composition Explained by the South Pole–Aitken Impact" (2024). Earth, Environmental and Planetary Sciences Theses and Dissertations. Brown Digital Repository. Brown University Library. https://repository.library.brown.edu/studio/item/bdr:2as29tph/

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Earth, Environmental and Planetary Sciences Theses and Dissertations

Theses and Dissertations for the Earth, Environmental and Planetary Sciences department.
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