Near-Earth object

A near-Earth object is an asteroid or comet whose orbit brings it into the region near Earth’s orbit around the Sun. Its orbit can cross or approach Earth’s orbit, but that alone does not mean an impact is imminent.

Asteroid: A small rocky or metallic body orbiting the Sun, smaller than a planet and distinct from a comet. Most near-Earth objects are asteroids, making this the main object type in the category.
Astrometry: The measurement of celestial positions and motions. Repeated astrometric positions establish a near-Earth object’s orbit.
Planetary defense: The detection and mitigation of natural space objects that could strike Earth. Near-Earth objects are the targets monitored and, if necessary, deflected by planetary defense.
99942 Apophis: A near-Earth asteroid discovered in 2004 that will pass safely close to Earth in 2029. Early calculations raised impact concern, while later observations ruled out a collision in 2029.
Asteroid impact prediction: The estimation of whether and when an asteroid could collide with Earth. Predictions depend on refining near-Earth object orbits and accounting for small forces.
Comet: An icy Solar System body that can release gas and dust as solar heating brings it near the Sun. Some near-Earth objects are comets whose elongated orbits enter Earth’s orbital region.
Orbit determination: The calculation of an orbit from observations of an object's position over time. A reliable orbit predicts future approaches and whether Earth’s path could be crossed.
Near-Earth Object Surveyor: A NASA space telescope mission designed to discover and characterize near-Earth objects using infrared observations. The mission is purpose-built to find objects that ground-based surveys can miss.
101955 Bennu: A carbon-rich near-Earth asteroid visited and sampled by NASA’s OSIRIS-REx mission. Bennu links orbital hazard assessment with direct study of asteroid composition.
Impact hazard: The risk of damage caused by a collision between a celestial object and a planetary surface. An object's size, speed, composition, and impact location determine its potential consequences.

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