Date of Degree

9-2016

Document Type

Dissertation

Degree Name

Ph.D.

Program

Earth & Environmental Sciences

Advisor(s)

Harold Connolly Jr

Committee Members

Michael Weisberg

John Chamberlain

Subject Categories

Astrophysics and Astronomy

Keywords

lunar impact, formation moon, oxygen isotope

Abstract

The goal of this research was to identify areas where deviations from the canonic Moon forming impact scenario (an impactor approximately 12% of the mass of the Earth merging with 100% accretion efficiency with a proto-Earth each of which has a differentiated homologous anatomy of 30% iron and 70% silicates) may greatly reduce the efficacy of the impact mass balance analytics used to determine the provenance of the impactor based on isotope data from terrestrial and lunar samples and physical data from high resolution SPH computer simulations.

Modeling the giant Moon forming impact is complicated by a lack of knowledge about the size, composition and origin of the impactor. During the impact the proto-Earth and impactor collide and merge forming the Earth and Moon with each having specific isotope values that are a blend of the stable isotopic signatures of the impacting bodies.

This research focused on four particular areas of concern; heterogeneity between the proto-Earth and the Earth, non-homologous impactor iron cores, the addition of an ice layer on the impactor and the importance of inefficient accretion (ejecta losses from the Earth during the collision). This research has shown that simple mass balance equations present an oversimplification of the mass balance relationships used for impact isotope analytics, particularly when the impactor deviates from the canonic scenario.

Through careful mathematical modeling of a four body system; two objects colliding (proto-Earth and impactor) forming two different objects (Earth and Moon), a comprehensive isotopic Four Body Mass Balance (4BMB) equation was developed, one which is capable of incorporating impactors which deviate from the canonic model.

Based on this research it is readily apparent that for lunar impactor fractions which are in the range indicated by SPH modeling (70% to 90% impactor in the Moon) changing the fraction of impactor’s iron core or accounting for inefficient accretion have a minimal effect on the resulting lunar isotope values and that the incorporation of a layer of ice on the impactor in the cases studied was the dominant factor.

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