Effect of yield curves and porous crush on hydrocode simulations of asteroid airburst

High entry speed (>25 km s À1 ) and low density (<2500 kg m À3 ) are the two factors that lower the chance of a meteoroid to drop meteorites. The 26 g carbonaceous (CM2) meteorite Maribo recovered in Denmark in 2009 was delivered by a bright bolide observed by several instruments across northern and central Europe. By reanalyzing the available data, we confirmed the previously reported high entry speed of (28.3 AE 0.3) km s À1 and trajectory with slope of 31°to the horizontal. In order to understand how such a fragile material survived, we applied three different models of meteoroid atmospheric fragmentation to the detailed bolide light curve obtained by radiometers located in Czech Republic. The Maribo meteoroid was found to be quite inhomogeneous with different parts fragmenting at different dynamic pressures. While 30-40% of the (2000 AE 1000) kg entry mass was destroyed already at 0.02 MPa, another 25-40%, according to different models, survived without fragmentation up to the relatively large dynamic pressures of 3-5 MPa. These pressures are only slightly lower than the measured tensile strengths of hydrated carbonaceous chondrite (CC) meteorites and are comparable with usual atmospheric fragmentation pressures of ordinary chondritic (OC) meteoroids. While internal cracks weaken OC meteoroids in comparison with meteorites, this effect seems to be absent in CC, enabling meteorite delivery even at high speeds, though in the form of only small fragments.

Section: Discussionmentioning

confidence: 99%

The Maribo CM2 meteorite fall—Survival of weak material at high entry speed

Borovička

Попова

Spurný

2019

“…; Register et al. ; Robertson and Mathias ) have been validated against the observed ground‐level ∆ P from Chelyabinsk (Aftosmis et al. ).…”

Section: Introductionmentioning

confidence: 99%

The frequency of window damage caused by bolide airbursts: A quarter century case study

Brown

Aftosmis

2018

We have empirically estimated how often fireball shocks produce overpressure (∆P) at the ground sufficient to damage windows. Our study used a numerical entry model to estimate the energy deposition and shock production for a suite of 23 energetic fireballs reported by U.S. Government sensors over the last quarter century. For each of these events, we estimated the peak ∆P on the ground and the ground area above ∆P thresholds of 200 and 500 Pa where light and heavy window damage, respectively, are expected. Our results suggest that at the highest ∆P, it is the rare, large fireballs (such as the Chelyabinsk fireball) which dominate the long‐term areal ground footprints for heavy window damage. The height at the fireball peak brightness and the fireball entry angle contribute to the variance in ground ∆P, with lower heights and shallower angles producing larger ground footprints and more potential damage. The effective threshold energy for fireballs to produce heavy window damage is ~5–10 kT; such fireballs occur globally once every 1–2 years. These largest annual bolide events, should they occur over a major urban center with large numbers of windows, can be expected to produce economically significant window damage. However, the mean frequency of heavy window damage (∆P above 500 Pa) from fireball shock waves occurring over urban areas is estimated to be approximately once every 5000 yr. Light window damage (∆P above 200 Pa) is expected every ~600 yr.

“…This porosity, which characterizes the initial physical structure of the meteoroid, can be either microscopic, that is, below the scale of our code's resolution, or in the form of macroscopic voids that may occupy one or more computational cells. A recent paper (Robertson and Mathias ) examines the role of porosity on the strength and crushing of a meteoroid; however, their model does not allow air to actually infiltrate into the body of the meteoroid. Initially retaining only the near‐vacuum of space at the starting altitude, the pore space controls the volume of air that may infiltrate into the body of the meteoroid.…”

Section: Introductionmentioning

confidence: 99%

Air penetration enhances fragmentation of entering meteoroids

Tabetah

Melosh

2017

The entry and subsequent breakup of the~17-20 m diameter Chelyabinsk meteoroid deposited approximately 500 kT of TNT equivalent energy to the atmosphere, causing extensive damage that underscored the hazard from small asteroid impacts. The breakup of the meteoroid was characterized by intense fragmentation that dispersed most of the original mass. In models of the entry process, the apparent mechanical strength of the meteoroid during fragmentation,~1-5 MPa, is two orders of magnitude lower than the mechanical strength of the surviving meteorites,~330 MPa. We implement a two-material computer code that allows us to fully simulate the exchange of energy and momentum between the entering meteoroid and the interacting atmospheric air. Our simulations reveal a previously unrecognized process in which the penetration of high-pressure air into the body of the meteoroid greatly enhances the deformation and facilitates the breakup of meteoroids similar to the size of Chelyabinsk. We discuss the mechanism of air penetration that accounts for the bulk fragmentation of an entering meteoroid under conditions similar to those at Chelyabinsk, to explain the surprisingly low values of the apparent strength of the meteoroid during breakup.