What is a meteor? What is an asteroid? Here are brief descriptions of the objects falling our way from far-away space.
Asteroids -- Pieces of debris left over from the formation of the solar system that are too small to be considered a planet, and that drift in an elliptical orbit around the sun. They range in size from 590 miles across to a speck of dust. The smallest yet detected by telescopes from Earth has been about 20 feet across. Most asteroids are made of clay and stony rocks; the rest are mostly silica and nickel-iron. There is an asteroid belt located between the orbits of the planets Mars and Jupiter.
Meteors -- Any asteroid that enters Earth’s atmosphere. Tens of thousands of space rocks do this on a regular basis. Most burn up and disintegrate into fine particles long before they get close to the surface. Depending on their size and angle, some give off a bright flash and trail, but most are what we describe as "shooting stars."
Meteorites -- The remnants of a meteor (estimated at about 10 feet in diameter) that reach the Earth’s surface, such as several small pieces that appear to have survived a fiery entry over eastern Russia Friday, breaking windows and causing other "airburst" damage that injured nearly 1,000 people.
Asteroid 2012 DA14 -- An asteroid about 150 feet in diameter that passed within 17,000 miles of Earth Friday afternoon, an astronomical close shave that caused no damage.
Comets -- Small icy bodies that are also solar system leftovers, different from asteroids because they contain frozen material. They are thought to have mainly formed in the outer part of our system and leave behind a coma, or tail, that points away from the sun as they follow wide orbits. Comets typically burn up if they strike the Earth, but fragments can make it through the atmosphere and large comets or asteroids can cause catastrophic damage.