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micrometeorite(mÿ-kroh-mee -tee-ŏ-rÿt) A cosmic dust particle of mass less than about 10–6 gram and diameter less than 0.1 mm. On impact with the Earth's atmosphere the heat absorbed by the particle from atmospheric friction is insufficient to raise it to boiling point. The ratio of heat radiated to heat absorbed is proportional to the inverse of the radius of a particle: those larger than 10–6 gram ablate and form meteors; smaller ones do not. The micrometeorite will be decelerated to a normal free-fall velocity and then drift to the surface of the Earth. On the Moon, however, no deceleration occurs and they impact the surface with the normal geocentric velocity.
A very small meteorite or meteoritic particle with a diameter generally less than a millimeter.