Are we prepared for an asteroid impact? A look at the science of detecting and potentially deflecting NEOs.

A near-Earth object (NEO) is any small Solar System body whose orbit brings it into proximity with Earth. By convention, a Solar System body is a NEO if its closest approach to the Sun (perihelion) is less than 1.3 astronomical units (AU). 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).

Most known PHOs and NEOs are asteroids, but a small fraction are comets. As of November 2023, there are over 33,000 known near-Earth asteroids and over a hundred short-period near-Earth comets (NEOCs). A number of solar-orbiting spacecraft have also been discovered. They are not considered NEOs.