Fragmentation and Wake Formation in Faint Meteors: Implications for the Structure and Ablation of Small Meteoroids

Meteors with peak magnitudes fainter than +2 are typically called faint meteors, resulting from the atmospheric entry and ablation of meteoroids less massive than 10-4 kg. The processes of luminous wake formation and fragmentation, which occur during ablation, are poorly understood for faint meteors, and are important constraints for models of meteoroid structure. The goal of this work is to improve understanding of these processes through analysis of high-resolution intensified video observations, and creation of a detailed meteoroid ablation model. In the first part of this work, thirty faint meteors observed with the Canadian Automated Meteor Observatory (CAMO) are analysed, revealing meteor trails with widths up to 100 m at heights above 110 km. These widths vary with height as the inverse of the atmospheric density, suggesting that formation of the wake is related to collisions between evaporated meteoric atoms and atmospheric molecules. Next, nine fragmenting faint meteors captured with CAMO are examined. Fragments from eight of the nine meteors are found to have transverse speeds up to 100 m s-1. These speeds are not explained by aerodynamic separation theory typically used for brighter meteors that fragment at lower heights. Instead, fragment separation by rotational breakup of the meteoroid or electrostatic repulsion are considered, giving meteoroid strength estimates up to 1 MPa. These strengths are typical of meteorite-producing meteoroids and are larger than expected for small meteoroids. Finally, a single-body ablation model, based on modelling collisions between the meteoroid, meteoric atoms, and atmospheric molecules, is devised to explain wake formation. Synthetic meteor trail widths and lengths, as well as light curves and deceleration profiles, are compared to observations of nine meteors from the first part of this thesis. The widths of simulated meteor wakes show good agreement with observations, but simulated wake lengths are too short. This suggests that collisional de-excitation of meteoric particles is a plausible process for wake formation, but also that meteoroid fragmentation likely increases the length of the meteor wake. Compared to observations, simulated light curves are longer, and simulated meteoroids experience less deceleration, suggesting that meteoroid fragmentation should be investigated in the next iteration of the model

Atmospheric Energy Deposition Modeling and Inference for Varied Meteoroid Structures

Asteroids populations are highly diverse, ranging from coherent monoliths to loosely-bound rubble piles with a broad range of material and compositional properties. These different structures and properties could significantly affect how an asteroid breaks up and deposits energy in the atmosphere, and how much ground damage may occur from resulting blast waves. We have previously developed a fragment-cloud model (FCM) for assessing the atmospheric breakup and energy deposition of asteroids striking Earth. The approach represents ranges of breakup characteristics by combining progressive fragmentation with releases of variable fractions of debris and larger discrete fragments. In this work, we have extended the FCM to also represent asteroids with varied initial structures, such as rubble piles or fractured bodies. We have used the extended FCM to model the Chelyabinsk, Benesov, Kosice, and Tagish Lake meteors, and have obtained excellent matches to energy deposition profiles derived from their light curves. These matches provide validation for the FCM approach, help guide further model refinements, and enable inferences about pre-entry structure and breakup behavior. Results highlight differences in the amount of small debris vs. discrete fragments in matching the various flare characteristics of each meteor. The Chelyabinsk flares were best represented using relatively high debris fractions, while Kosice and Benesov cases were more notably driven by their discrete fragmentation characteristics, perhaps indicating more cohesive initial structures. Tagish Lake exhibited a combination of these characteristics, with lower-debris fragmentation at high altitudes followed by sudden disintegration into small debris in the lower flares. Results from all cases also suggest that lower ablation coefficients and debris spread rates may be more appropriate for the way in which debris clouds are represented in FCM, offering an avenue for future model refinement