Dissertation/Thesis Abstract

Planetesimal Collisions in the Early Solar System and a Framework for Interpreting Iron Meteorite Cooling Rates
by Lyons, Richard J., III, Ph.D., The University of Chicago, 2020, 130; 27956715
Abstract (Summary)

Understanding how planets form is similar to a detective working a crime scene. The end results are all around us, but we need to look at the finer details and piece together the clues to find out how it all happened. When deciphering planet formation, difficulties lie in the fact that the planets we see today are the product of 4.5 billion years of dynamic and geologic evolution. Fortunately, the Asteroid Belt holds useful clues as it is populated with planetary building blocks (i.e. planetesimals) leftover from the epoch of planet formation. Meteorites, which are samples of these bodies, can provide key insights into the earliest evolution of the Solar System. Through meteorites, the types of collisions between these planetesimals during planet formation can be inferred and illuminate the dynamics at the time. If we can find the traces of these impacts hidden in meteorites, we can start to align the evidence and crack the case.

Iron meteorites provide a direct look at the processes that occurred on differentiated planetesimals such as their heating, separation of metal and silicate, cooling, and impact history. These effects are often treated independently of one another; however, we know that they would have been simultaneous and their concurrent effects need to be understood. Here, the effects impacts had in the early Solar System on the cooling histories of planetesimals are quantitatively investigated. This work shows, through the combination of impact and thermal models, that collisions can rapidly increase the cooling as well as create cooling rate variation (spanning many orders of magnitude in some cases) throughout the metal of differentiated bodies. The effectiveness of these impacts in causing such changes is dependent on the thermal and rheologic state of the impacted planetesimals, and subsequently, the time of the impact. The accelerated cooling also leads to nonlinear cooling of the metal in a planetesimal. Such nonlinear cooling would affect the formation of the Widmanstätten pattern, leading to differences when compared to the constant cooling rates of unimpacted bodies. These differences can be significant and can provide a means to identify the signatures of impacts in meteoritic samples. The traces of these impacts can, therefore, be searched for in the meteoritic record and could answer the many questions surrounding the formation of various meteorite groups (e.g. IAB, IIE, IVA, IVB). Determining what types of collisions are responsible for creating these tracers can also offer a means of probing the dynamics of the early Solar System. Thus, the framework developed here serves as another piece of the planet detective toolkit necessary to understand how planets formed.

Indexing (document details)
Advisor: Ciesla, Fred
Commitee: Campbell, Andrew, Davis, Andrew, Dauphas, Nicolas
School: The University of Chicago
Department: Geophysical Sciences
School Location: United States -- Illinois
Source: DAI-B 82/1(E), Dissertation Abstracts International
Source Type: DISSERTATION
Subjects: Geophysics, Astrophysics
Keywords: Cooling rates, Impacts, Iron meteorites, Planet formation, Planetesimal, Widmanstätten pattern
Publication Number: 27956715
ISBN: 9798662397217
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