A cosmic dust particle that has survived its passage through the Earth’s atmosphere without burning up as a meteor. Particles smaller than 0.1 mm in diameter, with masses under 10⁻⁶ g, are slowed by the upper atmosphere without melting, and drift down to the Earth’s surface. About one micrometeorite of diameter 0.1 mm falls on each square metre of the Earth’s surface per year, while for diameters of 0.01 mm the rate rises to about one per square metre per day. Micrometeorites can be collected in the stratosphere, providing samples of material from comets and asteroids for analysis. On the Moon and asteroids, the lack of an atmosphere means that micrometeorites impact the surfaces of these bodies at high speed.