Near Earth Asteroids

NEAs are Near Earth Asteroids, or in other words asteroids with orbits that bring them very close to Earth. These objects constitute the vast majority of NEOs (Near Earth Objects).
NEAs are divided into three main families, depending on the features of their orbits. In particular they are classified in three groups (Amor, Apollo and Atens) according to their perihelion and aphelion distances and their semi major axes (click here to see the general classification of NEOs).

 
The Apollo family includes most of Earth crossing asteroids and is made by asteroids with near-solar orbits. These are objects with highly eccentric orbits that cross the Earth's orbit.
The Amor family is made of asteroids with Mars-crossing but not Earth crossing orbits. They are believed to be formed by the interaction of Mars with the asteroids of the Apollo family.
The Aten family is made of asteroids with the orbit largely inside the orbit of the Earth.