A trail of debris laid down by a larger parent body, comprising small particles (meteoroids) which pursue a common orbit around the Sun. Most meteor streams originate from periodic comets, whose nuclei release dust when near perihelion. Over time, the meteoroids spread out along the comet’s orbit. When a meteor stream’s orbit approaches within about 0.1 au of the Earth, a meteor shower may occur. Filaments of debris released by the parent body over several successive returns give rise to variable activity from year to year, particularly in younger showers such as the Perseids; older streams such as the Taurids show a smoother, wider distribution of material, and less variable activity.