Physical Dispersions of Meteor Showers Through High Precision Optical Observations
Abstract
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.