Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Astronomy

Supervisor

Prof. Paul A. Wiegert and Prof. Peter G. Brown

Abstract

The past dynamical evolution of the meteoroid streams associated with comet 96P/Machholz is investigated. The goal is to obtain a coherent picture of the past capture of this large comet into a short period orbit, and its subsequent breakup hierarchy. In particular, the aim is to constrain the earliest epoch that this large first precursor started to supply meteoroids into the interplanetary space. The fragments and meteoroid streams of that past cometary decay constitute a wide multiplex of interplanetary bodies, knows as the 96P/Machholz complex. The largest presently surviving fragment is comet 96P/Machholz, followed by a large amount of debris including the Marsden and Kracht group of sungrazing comets, as well as at least one object of asteroidal appearance e.g., asteroid 2003 EH1.

It has been recognized that comet 96P/Machholz can give rise to eight different meteor showers within one Kozai secular cycle. These are the Quadrantids, daytime Arietids, Southern and Northern delta-Aquariids, kappa-Velids, theta-Carinids, alpha-Cetids and the Ursids. The first four showers are strong and well defined. The remaining four showers are weaker and less well constrained. In fact, while the activity of the Southern and Northern delta-Aquariids and kappa-Velids, theta-Carinids stands well above the sporadic meteor background, the existence of the alpha-Cetids and the Ursids, and their association with comet 96P/Machholz is uncertain.

Recently, some of these meteor showers have been associated with the Marsden group of sunskirting comets, based on orbital similarity and past dynamical evolution. The fact that these meteoroid streams are associated with more than one parent strongly suggest a possible genetic relationship between these bodies.

Using large-scale numerical simulations, the formation and past evolution of each individual meteoroid stream, associated with comet 96P/Machholz and the Marsden group of comets, is explored. Then the simulated shower characteristics are compared with observed ones as constrained by different meteor detection surveys (radar, TV, video, photographic and visual). \indent In the first part of this work, the formation and likely age of the Quadrantids, the strongest among the eight meteor showers, is examined. The Quadrantids are unusual with their very short duration of maximum activity (~17 hours) superimposed over a long-lasting weaker activity. The short duration of the peak activity indicates a narrow stream which on the other hand suggest that it must be young. Using numerical simulations it is demonstrated that the core of the Quadrantids is only 200 years old and is associated with asteroid 2003 EH1, while the broader activity is associated with comet 96P/Machholz. The possible nature of the parent, as a dormant or recently extinct comet, is emphasized.

The second part of the work focuses on the age and likely parent of the daytime Arietids meteor shower. Due to their daytime peak activity, the observational characteristics of the Arietids are mostly constrained by radar surveys. The association of the shower with comet 96P/Machholz, and more recent linkage to the Marsden group of sunskirters is examined. Numerical simulations fits to observations suggest that the the Marsden group of comets can not be the dominant parent of the stream, though they contribute to the peak of the shower. The major parent is comet 96P/Machholz and the age of the daytime Arietids is at least 10000 years.

The last part of this study investigates the origin and ages of the less-well constrained showers, the Southern and Northern delta-Aquariids, kappa-Velids, theta-Carinids, and the mis-associated alpha-Cetids and Ursids with comet 96P/Machholz. It is demonstrated that the gross features of the observed characteristics of the first four showers can be explained by comet 96P/Machholz while the Marsden group of comets contribute a small fraction to the peak activity of these showers. Furthermore, the association of the Northern delta-Aquariids with the Marsden group of comets, as previously suggested by several authors, is not supported by this study. Instead the bulk contributor to the shower is comet 96P/Machholz, and possibly another minor parent or parents not considered in this work. Furthermore, two showers were established as potential candidates for the misidentified alpha-Cetids and Ursids. These showers are the daytime lambda-Taurids and the much weaker December alpha-Draconids, though the last shower spatially overlaps with the November iota-Draconids, where their separation as individual showers is difficult. Lastly, the derived ages of all showers vary between 12000-20000 years, much older than previous estimates. When these shower age estimates are put into perspective, the observed characteristics of showers are consistent with a scenario of a capture of a large first precursor of the 96P complex circa 20000 BC and its subsequent fragmentation with a major break occurring around 100 AD as origin of the sunskirting comets.


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