Tagish Lake: The Survival Arithmetic of a Porous Carbonaceous Body over a Frozen Lake

This paper computes a complete entry budget for the Tagish Lake fireball, working only from published values and stated assumptions. The nominal body has a diameter of 5 metres at a bulk density of 900 kilograms per cubic metre, giving an incoming mass of 58.9 tonnes. At the published entry speed of 15.8 kilometres per second its kinetic energy is 1.76 kilotonnes of TNT equivalent. At the characteristic altitude of 30 kilometres the exponential atmosphere has a density of 0.019 kilograms per cubic metre, the ram pressure on the body is 4.74 megapascals, the stagnation heating flux is 3.75e+04 megawatts per square metre, and the aerodynamic deceleration is 161 times terrestrial gravity. The ram pressure first reaches representative material strengths at computed altitudes of 57.8, 41.2 and 29.6 kilometres for the weakest, intermediate and strongest cases examined. The recovered material, the pristine fragments collected from the frozen lake surface, amounts to 10 kilograms, which is 0.017 percent of the computed incoming mass. For scale, a single spherical fragment carrying that recovered mass would have a diameter of 17.8 centimetres, a terminal velocity of 117 metres per second, a fall time of 137 seconds from the end of the luminous path at 16 kilometres, and a wind drift of 1.37e+03 metres under a representative wind. All values are computed by the deposited program from the stated inputs; scenario calculations accompany every headline figure so that the sensitivity of each conclusion to its inputs is visible in the same record.