First holistic modelling of meteoroid ablation and fragmentation: A case study of the Orionids recorded by the Canadian Automated Meteor Observatory

Abstract

18 mm-sized Orionid meteoroids were captured in 2019 and 2020 by the Canadian Automated Observatory's mirror tracking system. Meteor position measurements were made to an accuracy of $\sim1$ m and the meteors were tracked to a limiting magnitude of about $+7.5$ at the faintest point. The trajectory estimation shows the intrinsic physical dispersion of the Orionid radiant is $0.400^{\circ} \pm 0.062^{\circ}$. An erosion-based entry model was fit to the observations to reproduce ablation and fragmentation for each meteor, simultaneously reproducing the light curve, the dynamics, and the wake. Wake observations were found to directly inform the grain mass distribution released in the modelled erosion. A new luminous efficiency model was derived from simultaneous radar and optical observations and applied in the modelling to improve its accuracy. The results show that the apparent strength of Orionids varies with radiant location and time of appearance during the period of shower activity. The average differential grain mass distribution index was 2.15, higher than found from in-situ estimates, possibly due to the evolution of the physical properties of meteoroids since ejection. All Orionids showed leading fragment morphology which was best explained by stopping the erosion at the peak of the light curve, leaving a non-fragmenting meteoroid with $\sim10\%$ of the original mass. The inverted Orionid meteoroid average bulk density of $\sim300$ kg m$^{-3}$, corresponding to porosities of $\sim90\%$, is consistent with in-situ measurements of larger dust particles by Vega-2 at 1P/Halley and Rosetta at 67P.