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Planetary radar projects (including JPL’s Goldstone Solar System Radar Group) are another key component of NASA’s NEO Observations Program. The vast majority of asteroid-tracking data, however, is collected by large NASA-funded observatories (such as Pan-STARRS, the Catalina Sky Survey, NASA’s NEOWISE mission and, in the future, NEO Surveyor).

This data is collected by observatories around the world, including significant contributions from amateur observers. The orbital positions of near-Earth objects come from the databases of the Minor Planet Center, the internationally recognized clearinghouse for small-body position measurements. CNEOS continuously monitors all known near-Earth objects to assess any impact risk they may pose. These objects are defined as asteroids that are more than about 460 feet (140 meters) in size with orbits that bring them as close as within 4.6 million miles (7.5 million kilometers) of Earth’s orbit around the Sun. The majority of near-Earth objects have orbits that don’t bring them very close to Earth, and therefore pose no risk of impact, but a small fraction of them – called potentially hazardous asteroids – require more attention. As more observations are made, the accuracy of an object's orbit improves dramatically, and it becomes possible to predict where an object will be years or even decades into the future – and whether it could come close to Earth. The orbit of each object is computed by finding the elliptical path through space that best fits all the available observations, which often span many orbits over many years or decades. Most near-Earth objects are asteroids that range in size from about 10 feet (a few meters) to nearly 25 miles (40 kilometers) across.

Near-Earth objects are asteroids and comets with orbits that bring them to within 120 million miles (195 million kilometers) of the Sun, which means they can circulate through the Earth’s orbital neighborhood. Managed for NASA at the Jet Propulsion Laboratory, the Center for Near Earth Object Studies ( CNEOS) accurately characterizes the orbits of all known near-Earth objects, predicts their close approaches with Earth, and makes comprehensive impact hazard assessments in support of the agency’s Planetary Defense Coordination Office at NASA Headquarters in Washington.