An asteroid is a solid chunk of space debris orbiting the sun; made of rock and metals it is considered inactive. Comets on the other hand can be quite active. Composed mainly of ice and smaller rocks, the “tail” we see is dust and gasses released from the ice by the sun’s energy. Meteoroids happen when asteroids collide; breaking into smaller pieces, or when the heat of the sun releases debris from a comet. A meteoroid that burns up in our atmosphere is called a meteor. If it makes impact; it becomes a meteorite.
Scientists consider anything under 100 LD (1 LD = distance from earth to the moon) a potentially hazardous asteroid (PHA). As of today there are 1366 PHA’s being monitored. On Feb. 15, 2013 DA14 – 57 metres, will pass between us and the moon at .9 LD. Behemoths like 3752 Camillo – 3.4 Km., and 1993 UC – 3.8 Km. will sail by on Feb. 12 and March 20 at 57.5 and 49 LD respectively.
There’s no sense in losing sleep over space junk; we can’t really do anything about it. Though reading my post on cosmic paintball is an interesting theory to ponder. Instead; thank your lucky stars the next time you wish on a falling star that it was a meteor and not a meteorite.