Doctor of Philosophy
Planetary Science and Exploration
Brown, Peter G.
Campbell-Brown, Margaret D.
Meteoroids ejected from comets form meteoroid streams which disperse over time due to gravitational perturbations and non-gravitational forces. When stream meteoroids collide with the Earth's atmosphere, they are visible as meteors emanating from a common point-like area (radiant) in the sky. Measuring the size of meteor shower radiant areas can provide insight into stream formation and age. The tight radiant dispersion of young streams are difficult to determine due to measurement error, but if successfully measured, the dispersion could be used to constrain meteoroid ejection velocities from their parent comets. The estimated ejection velocity is an uncertain, model-dependent value with significant influence on the prediction accuracy of meteor shower models which are operationally used by space agencies to mitigate the meteoroid impact risk.
The first part of this work consists of a theoretical investigation of achievable meteor radiant and velocity measurement accuracy using optical observation systems. From dynamical meteoroid stream modelling it has been estimated that a minimum radiant measurement accuracy of 0.1° is needed to begin to resolve the radiant structure of young meteor showers. Using a novel meteor trajectory simulator, it was found that this accuracy can be achieved using narrow field of view optical systems and a newly developed method of meteor trajectory estimation. The measurement accuracy of pre-atmosphere meteoroid velocities remains model-dependent because meteoroids may decelerate up to 750 m/s prior to becoming visible.
The second part of the work was observational and done using the Canadian Automated Meteor Observatory (CAMO). Four Electron Multiplying CCD cameras were used to observe the 2018 outburst of the Draconid meteor shower which had a radiant dispersion of 0.25°, consistent with simulations and previous high-precision measurements. A mass index of s = 1.74 ± 0.18 during the peak was estimated using a novel method. The CAMO mirror tracking system was used to observe the 2019 Orionids. For the first time, the Orionid radiant structure was accurately measured, showing indications of two stream branches. As part of the meteoroid modelling work to improve radiant and orbit measurements the compressive strengths of meteoroids were estimated through direct observations of fragmentation. The measured values were a good match to in-situ Rosetta measurements from comet 67P.
Summary for Lay Audience
When comets come close to the Sun, dust particles called meteoroids are ejected from the comet's surface and form meteoroid streams which initially closely follow the comet's orbit. Meteoroids within a stream drift away (disperse) from each other over time because they are pushed by Sun's radiation and pulled by the gravity of nearby planets. When stream meteoroids collide with the Earth's atmosphere, they are visible as meteor showers ("shooting stars") emanating from a common point-like area in the sky called the radiant. Observing meteors using video cameras from several locations enables us to compute their radiant and 3D trajectory in the atmosphere. Young streams (10s-100s years old) have tight radiant areas which are difficult to resolve because the measurements are usually not accurate enough. Knowing the true radiant dispersion can help to directly calculate the speed at which meteoroids were ejected from comets. Right now, the ejection speed is calculated from different theoretical models which do not agree with each other. The ejection speed is one of the most important parameters in meteor shower prediction models which are used by space agencies. During times of high meteor activity, space walks are suspended and satellites are reoriented to minimize the chance of impact. Historically, predicting the true activity of meteor showers has been challenging and several major meteor shower outbursts were not predicted because of unknown ejection speeds.
In this work, it was determined through meteoroid stream modelling that radiants should be measured with an accuracy of at least 0.1° to reveal the true radiant dispersion of young meteor showers. Using a new meteor shower simulator developed here, it was shown that the required accuracy can be achieved by existing optical meteor observation systems if our new method of computing meteor trajectories is used. Using very precise optical instruments that are a part of the Canadian Automated Meteor Observatory, real radiant dispersions of the Draconid and Orionid meteor showers were measured. The observed Draconid radiant positions match theoretical radiants well, and the structure of the Orionid radiant was revealed for the first time.
Vida, Denis, "Physical Dispersions of Meteor Showers Through High Precision Optical Observations" (2020). Electronic Thesis and Dissertation Repository. 6944.
Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.