Meteoroid bulk densities – a meteor shower survey

Meteoroid structure and bulk density are key indicators of its origin and thermal processing history. Physical properties of meteoroids with known parent bodies are of special interest and they provide an indirect way to probe the parent body itself (Flynn, 2004; Koten et al., 2019). The bulk density of shower meteoroids is a necessary assumption in dynamical simulations of meteoroid streams (Vaubaillon et al., 2005; Egal et al., 2019), with a major impact on the predicted particle sizes arriving on Earth (Vida et al., 2024) and the accuracy of meteor shower outburst predictions (Ye et al., 2014). The bulk density is also a key variable in spacecraft risk assessment, where the depth of hypervelocity impact craters scales with d ∝ ρ^4/27 (Moorhead et al, 2017).

This work discusses the latest meteoroid ablation and fragmentation modelling efforts using the Canadian Automated Meteor Observatory (CAMO) mirror tracking system (Vida et al., 2021). The instrument tracks meteors in real-time and provides 100 frame-per-second video at meter-scale spatial measurement accuracy. Meteors can be tracked to a limiting magnitude of +8. This high spatial resolution and sensitivity allow observing details of fragmentation and the wake profile.

A meteoroid ablation model which assumes meteoroids fragment gradually, by releasing micrometer-sized refractory grains from their surface (Borovička et al., 2007), was applied to observations of several major meteor showers. The model fits were performed manually using a trial-and-error method. The model is constrained by the observed light curve, dynamics (velocity and deceleration), and wake; the latter strongly informing the production rate and size distribution of released grains (Vida et al., 2024).

The method has so far been applied to 14 meteor showers (Egal et al., 2023; Buccongello et al., 2024; Pinhas et al., 2024) which cover a range of bulk densities from 250 to 1400 kg/m³: tau-Herculids, Orionids, July Pegasids, eta-Aquariids, Perseids, Leonids, Aurigids, Lyrids, Taurids, December Monocerotids, alpha-Capricornids, eta-Lyrids, Geminids, and Southern delta-Aquariids. The most surprising finding was that meteoroids from several showers have a two-part structure: a dense non-eroding core embedded in a softer matrix. This structure appears on both ends of the density range, in low-density (300 kg/m³) Orionids and in Southern delta-Aquariids which have bulk densities akin to carbonaceous chondrites (~1400 kg/m³).

In general, these new estimates are at variance with previous estimates by Kikwaya et al. (2011) who found that meteoroids of Jupiter-family comet (JFC) origin have chondritic densities (~3500 kg/m³). In contrast, new estimates for mean bulk densities of ~600 kg/m³ were found for JFC shower meteoroids and ~350 kg/m³ for Halley-type meteoroids, consistent with in-situ measurements.

Finally, an overview of the latest efforts to automate model fits and provide realistic parameter uncertainties is given.

 

References

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