“A near-Earth object (NEO) is an asteroid or comet orbiting the Sun with a perihelion distance of less than 1.3AU (1AU, an “astronomical unit”, is the mean distance between the Earth and the Sun, around 150million km)”.1Encyclopedia of the Solar System (Third Edition), 2014 Near-Earth Comets (NECs) are restricted to include only short-period comets.
“The vast majority of NEOs are asteroids, referred to as Near-Earth Asteroids (NEAs). NEAs are divided into groups (Atira, Aten, Apollo and Amor) according to their perihelion distance (q), aphelion distance (Q) and their semi-major axes (a)”.2JPL Center for NEO Studies (CNEOS)
“If a NEO’s orbit crosses the Earth’s, and the object is larger than 140 meters (460 ft) across, it is considered a potentially hazardous object (PHO)”.3Clark R. Chapman (May 2004). “The hazard of near-Earth asteroid impacts on earth”. Earth and Planetary Science Letters “Most known PHOs and NEOs are asteroids, but a small fraction are comets”.2JPL Center for NEO Studies (CNEOS)
