A near-Earth object (NEO) is an asteroid or extinct short-period comet in an orbit that may bring it close to Earth. NEOs have perihelion distances of less than 1.3 astronomical units and include near-Earth asteroids belonging to the Apollo, Amor and Aten groups. Three NEOs – Ganymed, Eros, and Eric – have diameters greater than 10 kilometers, while estimates suggest there may be at least 100,000 NEOs measuring 100 meters or more across. Many of these will collide with the inner planets over the next 10 million years or so.