Doctor of Philosophy
Planetary Science and Exploration
Wiegert, Paul A
Osinski, Gordon R
Earth is constantly bombarded by solar system objects of a wide variety of sizes, from micron-sized meteoroid stream and sporadic meteor dust, to meter-sized and larger meteoroids observed as fireballs. Fireball event characteristics directly point to the properties and structure of the parent body from which the meteoroid originated. In-atmosphere fireball data paired with in-space observations bring much context to both observations. This thesis centres on three published papers that grew out of my Masters project to identify precovery in-space images of meteoroids first observed as fireballs.
The first article describes the first successful identification of an in-space image of such a pre-fireball meteoroid, a US Government Sensor (USG) detection of an estimated 0.14 kiloton event in September 2020 over the Pacific Ocean. Analysis of the object's on-image streak along with USG, Geostationary Lightening Mapper (GLM), and infrasound observations allow us to characterize the object as a 2-3 meter diameter object of unusually low albedo and fragile structure, comparable to the 2008 TC3 Almahata Sitta impactor.
The second article presents an observing plan for an observationally favourable 2019 passage of a conjectured swarm of sub-kilometre diameter objects associated with the Taurid meteoroid stream. A confirmed Taurid Swarm (TS) would pose significant and continual risk to Earth. Observations of the proposed location of the TS will provide either verification or refutation of the swarm’s existence, and if found, for a determination of the risk presented.
The third article describes the second ever (at the time) observation of a Temporarily Captured Orbiter (TCO). In January 2014 the European Fireball Network observed a fireball event having the slowest ever recorded entry speed. Integrating the object's contact state back in time with the goal to identify precovery images, we discovered the object had made a close pass by the Moon, perturbing the object into an Earth impact from a prior somewhat chaotic low-speed Earth orbit.
The thesis concludes with four appendices describing the precovery image search process, a related work to identify parent bodies of fireball objects, modelling of meteoroid stream evolution, and a brief description of the software ClearSky used to implement these projects.
Summary for Lay Audience
Perhaps one occasionally lays awake at night wondering if a wayward space rock has Earth’s number. Perhaps one dreams of the future of our race exploring the stars. In either case, our future depends on an understanding of our Solar System environment and the huge number of large and small objects that inhabit near-Earth space. Knowing larger object positions, composition, and motion bring both the ability to predict hazardous Earth impacts and the knowledge needed to avert disaster by object deflection or destruction. On a smaller scale, trillions of dust particles stream along the paths of comets, slowly being tugged at by a myriad of forces, which over time blend into a massive random dust cloud throughout the Solar System. Spacecraft must travel through this cloud, and through the more dense streams, subjected to damaging dust particle impacts of huge energy due to the extreme velocities involved.
This thesis includes three published works, all pertaining to the meter-size or larger near-Earth objects. The first paper describes the first-ever successful retrieval of a ground-based telescopic image of an object that was first observed as an Earth-impacting fireball. A successful image discovery brings understanding of how an object's on-image appearance, its fireball event properties, and possibly its physical properties as a meteorite on the ground all interrelate. As well, such discoveries assist in evaluating the effectiveness of telescopic searches for impacting objects.
The second paper describes a search for a long-proposed swarm of larger objects embedded within the Taurid meteoroid stream and the related Taurid meteor shower. The Earth passes through this stream twice each year in June to July and October to December. If found to exist, this swarm of larger objects would present a considerable risk as it would pass near the Earth every few years.
The third paper describes a very unusual fireball event where the impact velocity of the object was the lowest impact velocity ever observed. Computation of the object's pre-impact trajectory showed that the object had likely been a temporary orbiter of the Earth and had been slung into an Earth impact by a near-Moon encounter.
Clark, David L., "Observation and Modelling of Meter-Class Earth impacting Asteroids" (2023). Electronic Thesis and Dissertation Repository. 9765.