Meteoritic dust from the atmospheric disintegration of a large meteoroid

Fate of a fireball Most of the mass of a meteoroid goes up (or comes down) in smoke: the largest of them can reach the ground but only 1–25% of the initial mass ever gets that far. The mystery of what happens to the rest can at last be addressed by direct observation, because one of the largest meteoroids to have entered the atmosphere during the past decade was caught in the act. As it disintegrated over Antarctica on 3 September last year, space-based infrared and light sensors detected the fireball and an 8-km-long debris trail. Spectral properties of this meteoric smoke reveal dust similar to olivine, a silicate mineral common in meteorites. Most of the dust consisted of particles about a thousandth of a millimetre in diameter, much larger than those normally regarded as being produced by atmospheric disintegration of rocky bodies. Much of the mass of most meteoroids entering the Earth's atmosphere is consumed in the process of ablation. Larger meteoroids (> 10 cm), which in some cases reach the ground as meteorites, typically have survival fractions near 1–25 per cent of their initial mass 1 . The fate of the remaining ablated material is unclear, but theory suggests that much of it should recondense through coagulation as nanometre-sized particles 2 . No direct measurements of such meteoric ‘smoke’ have hitherto been made 3 . Here we report the disintegration of one of the largest meteoroids to have entered the Earth's atmosphere during the past decade, and show that the dominant contribution to the mass of the residual atmospheric aerosol was in the form of micrometre-sized particles. This result is contrary to the usual view that most of the material in large meteoroids is efficiently converted to particles of much smaller size through ablation 4 . Assuming that our observations are of a typical event, we suggest that large meteoroids provide the dominant source of micrometre-sized meteoritic dust at the Earth's surface over long timescales.