... Every 33 years or so, the comet returns to the inner solar system and releases material that forms into a new dust trail. ... For example, in 2001 November and again in 2002 November , the Earth passed very near the centre of the trail released at the 1866 return (i.e. 4 revolutions of the comet ago), as well as near other trails, producing meteor storms. The following diagram shows the position of the 6 youngest Leonid dust trails when the Earth traverses the Leonid stream in 2003 November. ...