In 1961, the IAU defined meteoroids as a class of solid interplanetary objects distinct from asteroids by their considerably smaller size. This definition was useful at the time because, with the exception of the Tunguska event, all historically observed meteors were produced by objects significantly smaller than the smallest asteroids then observable by telescopes. As the distinction began to blur with the discovery of ever smaller asteroids and a greater variety of observed NEO impacts, revised definitions with size limits have been proposed from the 1990s. In April 2017, the IAU adopted a revised definition that generally limits meteoroids to a size between 30 μm and 1 m in diameter, but permits the use of the term for any object of any size that caused a meteor, thus leaving the distinction between asteroid and meteoroid blurred.
In 1961 the IAU defined meteoroids as a class of solid interplanetary objects distinct from asteroids by their considerably smaller size This definition was useful at the time because with the exception of the Tunguska event all historically observed meteors were produced by objects significantly smaller than the smallest asteroids then observable by telescopes As the distinction began to blur with the discovery of ever smaller asteroids and a greater variety of observed NEO impacts revised definitions with size limits have been proposed from the 1990s In April 2017 the IAU adopted a revised definition that generally limits meteoroids to a size between 30 μm and 1 m in diameter but permits the use of the term for any object of any size that caused a meteor thus leaving the distinction between asteroid and meteoroid blurred