El peligro de impacto asociado a grandes meteoroides procedentes de la fragmentación de asteroides y cometas

Resumen

Large meteoroid fragments disrupted from asteroids and comets may encounter the Earth along their orbits, posing extremely hazardous scenarios. Contemporary events like Chelyabinsk (2013), Carancas (2007) or Tunguska (1908) demonstrated that meteoroids in the diameter range of 1 to 100 m can devastate large areas and injure local population through the associated energetic blast, or even produce casualties due to localized crater excavation. Despite the relatively low frequency of these events, they have become a major concern within space agencies and other planetary defense initiatives which are currently developing impact mitigation tactics. This is in line with the growing popularity of this subject in the scientific community. The number of yet unresolved questions underlying the pre- and impact physics motivates the work carried out in this thesis. The study of meteoroids that encounter the terrestrial atmosphere provides valuable clues about their progenitors, their delivery mechanisms to Earth, and their ability to threaten our planet. This thesis starts by exploring the complexity of meteoroid dynamics through two exceptional phenomena. On the one hand, a limited number of meteoroid dust trails detached from the comet 8P/Tuttle 620 years ago impact the Earth when the parent comet is in its aphelion, thus increasing the activity of the annual Ursid meteor shower. Aphelion-related increases in a meteor shower activity are uncommon and hence the Ursids offer a new perspective of orbital mechanics. On the other hand, meteorite falls, like Annama, can be orbitally linked to celestial bodies if their atmospheric trajectories are accurately recorded. Exploring these parental relationships offer the opportunity to overcome the uncertainties emerged from the short-term orbital evolution of near-Earth objects and ultimately predict future impacts. The second part of this thesis focuses on the characterization of the atmospheric flight of a meteoroid. While up to-date re-entry models that account for the meteoroid ablation and fragmentation are common, no observational or modelling studies have resolved the intricacies associated with the mesosphere and lower thermosphere region for meteoroids travelling at hypersonic velocities and in rarefied gas flow conditions. This thesis presents the first observational validation of the flight flow regimes of centimeter-sized meteoroids and provides a new insight into the consequences for the meteoroid flight physics due to the generation of a shock wave. Meteoroid shock waves are also intimately related to the meteoroid energy deposition at different heights, which can alternatively be stated from the analysis of the terminal height of the meteoroid’s trajectory. A new approach capable to precict the terminal heights is outlined in this thesis. The results show that, besides the great accuracy achieved, the calculated terminal heights are a valuable input to the derivation of atmospheric flight parameters. Furthermore, the approach taken provides a new way of classifying impacting meteoroids that improve previous classification scales. Finally, a discussion of the implications of the previous analysis to impacting bodies of different sizes is carried out. Since Earth impacts by meter-sized or smaller bodies are more frequent, the study of sub-metric meteoroids provides a wide catalogue of events that can be crucial to understand the meteor physics. Being able to extrapolate the behaviour of these bodies to asteroid sizes can provide new clues on the underlying physics and make predictions concerning the degree of hazard associated with energetic events. The results of this work also provide feedback and an alternative approach to current and foreseen numerical simulations that were seen in the past as the only way to deal with these challenging encounters.