The Dynamical Evolution of the Inner Solar System

Carlisle A Wishard, Purdue University

Abstract

The solar system that we live in today bears only a passing resemblance to the solar system that existed 4.5 billion years ago. As our young star shed the gas nebula from which it was born, a disk of dust and rocky bodies emerged in the space between the Sun and Jupiter. Over the next hundred million years, this planetary disk evolved and gave rise to the terrestrial planets of the inner solar system. Clues left behind during this early stage of evolution can be seen in the orbital architecture of the modern planets, the cratering records of rocky bodies, and the signatures of the solar system’s secular modes.Past works in the fields of terrestrial planet accretion and solar system evolution typically do not include collisional fragmentation. While the mechanics of collisional fragmentation are well studied, the incorporation of this processes into simulations of terrestrial planet formation is computationally expensive via traditional methods. For this reason, many works elect to exclude collisional fragmentation entirely, improving computational performance but neglecting a known process that could have played a significant role in the formation of the solar system. In this dissertation, I develop a collisional fragmentation algorithm, called Fraggle, and incorporate it into the n-body symplectic integrator Swiftest SyMBA. Along with performance enhancements and modern programming practices, Swiftest SyMBA with Fraggle is a powerful tool for simulating the formation and evolution of the inner solar system.In this dissertation, I use Swiftest SyMBA with Fraggle to study the effect of collisional fragmentation on the accretion and orbital architecture of the terrestrial planets, as well as the cratering record of early Mars. I show that collisional fragmentation is a significant process in the early solar system that creates a spatially heterogeneous and time-dependent population of collisional debris that fluctuates as the solar system evolves. This ever-changing population results in cratering records that are unique across the inner solar system. The work presented in this dissertation highlights the need for independent cratering chronologies to be established for all rocky bodies in the solar system, as well as the need for future models of solar system accretion to include the effects of collisional fragmentation.While the cratering records and orbits of the terrestrial planets are two means by which to study the solar system’s ancient past, analysis of the evolution of the secular modes of the solar system offers a third method. A secular mode arises due to the precession of the orbit of a planet over time. Each body’s orbit precesses at a specific fundamental frequency, or mode, that has the power to shape the orbital architecture of the solar system. I show that jumps in the eccentricity of Mars can trigger short-lived power sharing relationships between secular modes, resulting in periods in which the strength and fundamental frequencies of modes fluctuates. While evidence of these past jumps in Mars’ eccentricity would likely not be visible today in the secular modes of the inner solar system, the work presented in this dissertation poses additional questions. In particular, questions related to other possible triggers of power sharing relationships, as well as the effects of power sharing relationships on the stability of small bodies during these periods of fluctuation, are particularly compelling.

Degree

Ph.D.

Advisors

Freed, Purdue University.

Subject Area

Astronomy

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