What is an asteroid?

As asteroids (Greek ἀστήρ, aster "star" and the suffix-affirmation "similar"), minor planets or planetoids small objects are known, which move on Keplerian orbits around the sun.
So far, 559 757 asteroids in the solar system are known (as of 2 August 2011), although the actual number may well be in the millions. However, only few of them have more than some 100 kilometers in diameter, so that they assume because of their own gravity, a round shape and then among the dwarf planets.

Most asteroids whose orbits run in part within that of Mars, are called near-Earth asteroids. Because of a theoretical risk of collision with Earth is some years since a systematic search for them. The search program is successful Lincoln Near EarthAsteroid Research (LINEAR). More search programs are NEAT and LONEOS

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