TAGISH LAKE METEORITE FALL : INTERPRETATION OF FIREBALL PHYSICAL CHARACTERISTICS.

We have analyzed available instrumental and eyewitness records associated with the fireball leading to the fall of the Tagish Lake meteorite. Initial chemical and physical studies of this carbonaceous chondrite have shown it to be unique. It is one of the most primitive meteorites yet recovered and extremely friable. By determining the original bodies trajectory, velocity and physical breakup in the atmosphere we can characterise the fireball as intermediate between Type II and Type IIIa, following the classification of Ceplecha et al. Modelling of the object suggests an initial porosity of the pre-atmospheric body in the range 40-60%. The initial fragmentation occurred under less than 0.3 MPa dynamic pressure. Determination of Tagish Lake's orbit suggests a nominal linkage to parent bodies in the main asteroid belt, though association with short-period comets cannot be strictly excluded. It is suggested that Tagish Lake represents an intermediate object between chondritic asteroids and cometary bodies and our results are consistent with a linkage to D-class asteroids based on results from reflectance-spectra work