NEO fireball diversity: energetics-based entry modeling and analysis techniques

Abstract

We have examined the behavior of a number of bolides in Earth's atmosphere from the standpoint of recent entry modeling techniques. The entry modeling has been carried out including a triggered progressive fragmentation model (TPFM) which maintains a maximum drag orientation for the fragments in either the collective or a non-collective wake limit during entry (ReVelle 2004). Specifically in this paper, we have proposed a new method of estimating the terminal bolide mass and have compared it against the corresponding single-body mass loss prediction. A new expression for the terminal mass is proposed that corrects the mass of the body for the changing mass to area ratio during the fragmentation process. As a result of this new work we have found two very interesting features that correspond very closely to those found from a direct analysis of the observational data. These include an instantaneous mass that closely resembles that directly observed and an ablation coefficient behavior that also strongly resembles meteor observations (such as those found recently by Ceplecha & ReVelle 2005). During fragmentation, the apparent ablation coefficient has now been shown to decrease dramatically approaching the intrinsic ablation coefficient proposed by Ceplecha & ReVelle (2005). In our modeling we have assumed a breakup into equal size fragments that are consistently and progressively multiples of two of the original unbroken leading piece. Had we assumed a multitude of many much smaller pieces that made up the totality of the original body, our predicted ablation coefficient would indeed have approached the very small intrinsic ablation parameter values predicted by Ceplecha and ReVelle. This is especially evident in the case of Sumava, but is also true in a number of other cases as well. The bolides whose properties have been modeled using our detailed entry code including a prediction of the panchromatic luminosity consist of the 1965 respectively (Klekociuk et al. 2005). A self-consistent assessment of the detailed properties of each of the fireballs was made using all available information for each event. In the future, more reliable estimates of all of the necessary source parameters (including their overall degree of bulk porosity) will be made if all channels of information are reliably retrieved for bolide events (channels such as acoustic-gravity waves and specifically its infrasound emission, seismic waves, satellite optical and IR data, ground-based spectroscopy, ground-based photometry and radiometry, VLF radiation, meteorite fragment recovery, etc.).

Park Forest (L5) and the asteroidal source of shocked L chondrites

“…This is compatible with the sizes determined from fireball models with significant porosity (40%, Brown et al. ; 20%, ReVelle ). Within this 0–40% porosity range, the resulting pre‐atmospheric mass of Park Forest is ~2–6 tons.…”

“…() implies (at a density of 0.6 × 3.4 g cm −3 = 2.04 g cm −3 ) a size of 191 g cm −2 , which is compatible with our results within their uncertainties, as well as with the size derived from the dynamical approach. ReVelle () suggested another model with a total mass of approximately 3400 kg and a porosity of 20%, resulting in a size of 181 g cm −2 , which is again compatible with the radionuclide, noble gas, and dynamical results. Therefore our results, as well as two models from literature, can be brought to agreement if Park Forest had a pre‐atmospheric size close to 180 g cm −2 with a porosity of 0–40%, resulting in corresponding ranges of 0.53–0.88 m in radius, 2.0–3.4 g cm −3 in density, and 1730–5870 kg in pre‐atmospheric mass.…”

“…). There is a wide range of estimates for the pre‐atmospheric mass of Park Forest, ranging from 3400 kg (ReVelle ) to 1.8 × 10 4 kg (Brown et al. ), with a preferred value of (1.1 ± 0.3) × 10 4 kg given by Brown et al.…”

Fall, recovery, and characterization of the Novato L6 chondrite breccia

“…In contrast, the recovered meteorite fragments' observed average porosity was <5%. Subsequent work revisited the luminous efficiency for given mass loss and estimated the meteoroid porosity at only 20%, corresponding to a approximately 50% lower mass (ReVelle ). Rapid late‐stage or continuous mechanical surface spallation of otherwise intact fragments, as observed for Novato, could account for the anomalous luminous efficiency of Park Forest.…”

Analyzing Meteoroid Flights Using Particle Filters

“…Multiple approaches have been taken to handle these unknowns in fireball trajectory analysis. The manually intensive method of Revelle [2007] is based on the brute force least squares approach of Ceplecha and Revelle [2005]. It does include the luminosity of the fireball (derived from manual interpretation of a light curve) as a proxy for mass loss and solves for fragmentation as well as σ and κ.…”