near-Earth object

A near-Earth object (NEO or if specifically an asteroid, near-Earth asteroid or NEA) is an object, such as a comet or asteroid, in solar orbit that passes near Earth. An Earth-crossing asteroid (ECA) is an asteroid whose orbital path crosses that of Earth. A fast moving object (FMO) is an observed astronomical object that appears moving very fast, undoubtedly a NEO. All these are of special interest because of the potential for a future impact with Earth (those most likely are termed potentially hazardous objects, PHOs, or if specifically asteroids, potentially hazardous asteroids, PHAs), and a number of surveys aim to identify them:

• Catalina Sky Survey.
• LINEAR.
• LONEOS.
• Pan-STARRS.

Near-Earth objects are also useful destinations for space probes, such as OSIRIS-REx visiting 101955 Bennu. Comets and asteroids passing close to Earth are among the easiest to reach.

NEOs are also classified according to a comparison of their orbits with that of Earth, each type referred to by the name of the first such asteroid discovered:

• Aten - ECA with semi-major axis smaller than Earth's and aphelion large enough to cross Earth's orbit.
• Apollo - ECA with semi-major axis larger than Earth's and perihelion small enough to cross Earth's orbit.
• Amor - passes close to Earth's orbit from the outside but does not cross it.
• Atira or Apohele or IEO (for inner-Earth object) passes close to Earth's orbit from the inside but does not cross it.

The independent term Arjuna has been coined for any of these with orbits much like Earth's.