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P.G. Brown (EES-8, Los Alamos National Laboratory, Los Alamos, NM 87545 USA), A.R. Hildebrand (Department of Geology and Geophysics, University of Calgary, Calgary AB T2N 1N4 Canada), D.O. ReVelle (EES-8, Los Alamos National Laboratory, Los Alamos, NM 87545 USA)
The Tagish Lake meteorite fell in northern British Columbia, Canada on 18 Jan 2000. It has been classified as a C2 ungrouped carbonaceous chondrite and displays many unique properties (Brown et al. 2000). Most notable is the probable linkage of Tagish Lake to D-class asteroids based on spectral reflectance (Hiroi et al. 2001). We have analyzed the associated fireball data consisting of eyewitness reports, video and photographic observations of the associated dust cloud, seismic signals and satellite records. These data are interpreted in the context of a new ablation model explicitly accounting for porosity of the initial body. From these data we find that the fireball physical behavior is intermediate between type II (associated with carbonaceous chondrites) and type IIIa (associated with strong cometary material) fireballs, following the classification system of Ceplecha et al. (1998). Measured porosities of two recovered fragments measure 37±6%-40±10% with bulk densities near 1.6 ± 0.1 gcm-3. Our modelling suggests the initial Tagish Lake meteoroid to have had a minimum porosity of ~50%. The initial fragmentation of Tagish Lake occurred under 0.3 Mpa of dynamic pressure, at the low-strength end of the fireball spectrum (Ceplecha 1993). The initial mass of the meteoroid is estimated to be 65±15 tonnes. The orbit of the Tagish Lake meteoroid suggests a nominal linkage to asteroidal bodies, though the Tisserand value (3.6) and 1/a=0.5 does not rule out classification as an Encke-type cometary orbit (Levison, 1996). In terms of physical behavior, these data suggest Tagish Lake represents a body intermediate between chondritic asteroids and cometary bodies. Inferences from the fall of Tagish Lake thus allow a means to assess information on physical parameters such as strength, density, composition and porosity for a ~4m D-class NEA using ground-truth data.
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The author(s) of this abstract have provided an email address for comments about the abstract: pbrown@lanl.gov