Internal structure and physical properties of the Asteroid 2008 TC3 inferred from a study of the Almahata Sitta meteorites

Abstract-As part of a large-scale survey of meteorite bulk and grain densities, porosities, and magnetic susceptibilities, we measured these properties for 174 stones from 106 achondritic meteorites. These include four lunar meteorites, 15 stones from 10 shergottites, nakhlites, and chassignites (SNCs), 96 stones from 56 howardites, eucrites, and diogenites (HEDs), 17 stones from nine aubrites, two angrites, and 16 stones from 10 ureilites, four stones of three acapulcoites, as well as four stones of three lodranites, and 15 stones from eight primitive achondrites. Those meteorites derived from basalts and crustal material of differentiated parent bodies have lower densities and magnetic susceptibilities, on an average, than the more primitive achondrites, which have a higher percentage metal. A notable exception is the one chassignite in the study (Chassigny), which has a high grain density of 3.73 ± 0.04 g cm )3 . Ureilites have magnetic susceptibilities consistent with primitive achondrites, but lower grain densities. Porosities do not vary considerably between most of the groups, with most stones 5-14% porous, although on an average, ureilites and brachinites have lower porosities, with most stones less than 7% porous. For primitive achondrites, the higher metal content causes finds to exhibit weathering effects similar to what is observed in ordinary chondrites, with a reduction in grain density, magnetic susceptibility, and porosity as compared with unweathered falls. For lunites, SNCs, and HEDs, no such effect is observed. We also observe that grain density and magnetic susceptibility used in conjunction distinguish shergottites, nakhlites, and chassignites from each other. Shergottites and nakhlites have low grain densities (averaging 3.31 and 3.41 g cm )3 , respectively) whereas Chassigny is 3.7 g cm )3 . In magnetic susceptibility, shergottities and chassignites are similar (averaging 2.85 and 2.98 in log units of 10 )9 m 3 kg )1 , respectively) with nakhlites averaging higher at 3.42.

Section: Resultsmentioning

confidence: 99%

Density, porosity, and magnetic susceptibility of achondritic meteorites

Macke

Britt

Consolmagno

2011

“…Analysis of the pre‐entry observations and the meteorite falls also indicate that the body had significant macro porosity (Kohout et al. ). The meteor was observed to break up high in the atmosphere, indicating a weak body and consistent with a weakly bound rubble pile (Borovička and Charvat ; Popova et al.…”

Section: Observational Evidence For Cohesionmentioning

confidence: 99%

The strength of regolith and rubble pile asteroids

Sánchez

Scheeres

2014

217

176

Abstract-We explore the hypothesis that, due to small van der Waals forces between constituent grains, small rubble pile asteroids have a small but nonzero cohesive strength. The nature of this model predicts that the cohesive strength should be constant independent of asteroid size, which creates a scale dependence with relative strength increasing as size decreases. This model counters classical theory that rubble pile asteroids should behave as scale-independent cohesionless collections of rocks. We explore a simple model for asteroid strength that is based on these weak forces, validate it through granular mechanics simulations and comparisons with properties of lunar regolith, and then explore its implications and ability to explain and predict observed properties of small asteroids in the NEA and Main Belt populations, and in particular of asteroid 2008 TC 3 . One conclusion is that the population of rapidly rotating asteroids could consist of both distributions of smaller grains (i.e., rubble piles) and of monolithic boulders.

“…Models use the parameters in Table 1; stars indicate onset of pancaking at breakup altitude. distribution centered about q avg = 3257 kg m À3 with a standard deviation q std = 510 kg m À3 (Medvedev et al 1985;Boroviĉka et al 2003;Britt and Consolmagno 2003;Llorca et al 2005;Hildebrand et al 2006;Jenniskens et al 2009;Kohout et al 2011;Popova et al 2011). The corresponding quantile function for the solid density of the impactor q si is:…”

Section: Density and Strengthmentioning

confidence: 99%

A numerical assessment of simple airblast models of impact airbursts

Collins

Lynch

McAdam

et al. 2017

Abstract-Asteroids and comets 10-100 m in size that collide with Earth disrupt dramatically in the atmosphere with an explosive transfer of energy, caused by extreme air drag. Such airbursts produce a strong blastwave that radiates from the meteoroid's trajectory and can cause damage on the surface. An established technique for predicting airburst blastwave damage is to treat the airburst as a static source of energy and to extrapolate empirical results of nuclear explosion tests using an energy-based scaling approach. Here we compare this approach to two more complex models using the iSALE shock physics code. We consider a moving-source airburst model where the meteoroid's energy is partitioned as twothirds internal energy and one-third kinetic energy at the burst altitude, and a model in which energy is deposited into the atmosphere along the meteoroid's trajectory based on the pancake model of meteoroid disruption. To justify use of the pancake model, we show that it provides a good fit to the inferred energy release of the 2013 Chelyabinsk fireball. Predicted overpressures from all three models are broadly consistent at radial distances from ground zero that exceed three times the burst height. At smaller radial distances, the moving-source model predicts overpressures two times greater than the static-source model, whereas the cylindrical line-source model based on the pancake model predicts overpressures two times lower than the static-source model. Given other uncertainties associated with airblast damage predictions, the static-source approach provides an adequate approximation of the azimuthally averaged airblast for probabilistic hazard assessment.