Meteoroid structure and fragmentation

Abstract

The physical composition and structure of meteoroids gives us insight into the formation processes of their parent asteroids and comets. The strength of and fundamental grain sizes in meteoroids tell us about the environment in which small solar system bodies formed, and the processes which built up these basic planetary building blocks. The structure of meteorites can be studied directly, but the set of objects which survive entry through the atmosphere is biased toward large, strong objects with slow encounter speeds.Fragile objects, small objects and objects with high relative speeds are very unlikely to survive impact with the atmosphere. Objects between 100 microns and 1 meter, which are not strong enough to survive the ablation process, must be studied by radar or optical methods.Large meteoroids, which produce bright fireballs, are generally studied by investigating their compressive strength when they fragment, and their strength can also be inferred indirectly from their end heights.Fragmentation in faint meteors can be inferred from interference in radar observations, or observed directly with high-resolution optical systems. Me-teor light curves, begin heights and time-evolving spectra can also be used to infer meteoroid structure. This paper presents a review of the meteor observation methods currently used to infer the structure and fragmentation of meteoroids in the millimeter to meter size range, and the current state of understanding these observations have given us.

Occurrence and Altitude of the Long‐Lived Nonspecular Meteor Trails During Meteor Showers at High Latitudes

“…One can see that larger porosity is attributed to H‐type streams, Leonids, Orionids, and η‐Aquariids (the latter two have the same parent, Halley comet, so that we assume that they have similar properties, although the data for η‐Aquariids were not found in the literature). This result is expected (e.g., Campell‐Brown, 2019). Less dense (crumbly and porous) meteoroids may be more easily disrupted in less dense air at higher altitude into a swarm of smaller particles (aerosols), which is necessary for LLNS echoes.…”

“…Namely, the P‐type shower meteoroids (Quadrantids, Arietids or/and Daytime ζ‐Perseids, Geminids, and Ursids) have the lowest velocity, 29–39 km/s, for the PH‐type (Lyrids and Perseids) the velocity is higher, 47–61 km/s, and the highest velocity, 65–67 km/s, is during the H‐type showers (Orionids and Leonids). It is known that meteoroids entering the atmosphere at higher speed ablate in less dense air, hence, at a higher altitude (e.g., Campell‐Brown, 2019). For instance, modeling shows that intensive evaporation of meteoroids larger than 0.2 cm with entry velocity 70 km/s starts at an altitude of about 115 km, whereas similarly sized meteoroids with a velocity 30 km/s evaporate below 95 km (Popova et al, 2019).…”

Atomic‐Scale Simulations of Meteor Ablation

“…Fragmentation models are often directly fit to optical observations (Campbell‐Brown, 2019). Some models use the energy transfer coefficient as a free parameter (Vojáček et al, 2019) or a constant value less than 1 (Campbell‐Brown, 2019). The energy transfer coefficient is another material‐, velocity‐, and altitude‐dependent parameter that should be taken into account when modeling light curves to extract physical parameters from observations.…”

“…As discussed in the introduction, we are not looking specifically at melting within the thermal ablation process. Fragmentation models are often directly fit to optical observations (Campbell‐Brown, 2019). Some models use the energy transfer coefficient as a free parameter (Vojáček et al, 2019) or a constant value less than 1 (Campbell‐Brown, 2019).…”

Ablation Rates of Organic Compounds in Cosmic Dust and Resulting Changes in Mechanical Properties During Atmospheric Entry

“…However, the pyrolysis of carbon and sulfur compounds in cosmic dust at temperatures below 1800 K (i.e., prior to melting), which can potentially lead to meteoric fragmentation if sufficiently rapid (Campbell‐Brown, 2019), does not appear to have been considered in detail. The fragmentation of meteoroids as small as ∼2 mm in radius has been observed directly using high‐speed meteor video (Campbell‐Brown, 2019; Vojacek et al., 2019); observations at the Canadian Meteor Observatory (CAMO) show that a large majority (>90%) of the recorded meteors fragmented (Campbell‐Brown, 2019). However, there are two points to keep in mind.…”