The pre-atmospheric size of the Martian meteorite ALH 77005 progenitor

An upper mass estimate of 30 kg, corresponding to a diameter of order 26 cm, is derived for the progenitor meteoroid to Martian meteorite ALH77005. This estimate is derived upon the application of a cooling time model, constrained so as to allow for the observed partial recrystallization of plagioclase within the meteorite's interior. This new estimate for the size of the progenitor to ALH77005 is some 2–3 times larger than that previously assumed by earlier researchers. Uncertainty in the value of the thermal diffusivity term appropriate to Martian meteorite material results in the cooling time model allowing for a possible pre-cursor mass range of 25 and 110 kg. An Earth atmosphere interaction model has been applied against the cooling time model mass range, under the constraint that the most likely Earth encounter speed is less than 20 km/s, and that the parent body does not fragment in the Earth's atmosphere. It is through the consideration of the fireball ablation model that the eventual upper bound of 30 kg is obtained.